Mahui

A novel thermal radiated hot‐cast method (THCM) is specially designed to fabricate highly efficient perovskite solar cells (PSCs) in ambient air. THCM creates constant temperature and ultralow relative humidity fields for perovskite growth, and is a universal protocol suitable for both inverted and regular PSCs, of which the champion power conversion efficiency of 17.2 and 19.1% is achieved, respectively.

Perovskite solar cells (PSCs) have developed rapidly in the past few years. However, highly efficient PSCs prepared in ambient air have remained intractable, since the crystallization and film morphology of perovskite are highly sensitive to moisture. Here, a thermal radiated hot‐cast method (THCM) to prepare high quality perovskite films in ambient air is introduced. The proposed THCM not only eliminates the temperature gradient across the perovskite film, but also forms a significantly reduced and constant relative humidity field at the local space above the substrate (ca. 6%); these conditions result in a smooth, compact, oriented perovskite film with largely reduced grain boundaries. THCM is a universal protocol, based on the application to the devices with both inverted and regular architectures, and it enables improved J–V performance with largely reduced hysteresis. The champion power conversion efficiencies of 17.2% for inverted and 19.1% for regular devices are achieved by THCM. These are comparable to the top efficiencies of fully air‐processed PSCs, demonstrating that THCM is a promising protocol for commercialization of PSCs in the near future.

DMSO‐molecule‐control is demonstrated to enhance the morphological and electronic qualities of Cs‐(FAPbI₃)_0.85(MAPbBr₃)_0.15 absorbers, thus increasing the efficiency (reaching 19.4%) and boosting the long‐term stability (retaining 90% of the initial efficiency after 50 days in ambient air) of 1 cm² sized planar perovskite solar cells.

While interfacial and grain‐boundary passivation presently attract enormous research interest for perovskite solar cells (PSCs), the improvement of Cs‐(FAPbI₃)_X(MAPbBr₃)_Y bulk quality still lacks systematical study, especially for constructing polycrystalline layers in planar configurations. Here, a DMSO‐molecule‐process for improving the quality of Cs‐(FAPbI₃)_0.85(MAPbBr₃)_0.15 is developed, where the molar ratio of precursors, the kind of anti‐solvents, and speed‐time profiles are found critical. The optimized treatment significantly enhanced the crystal orientation, grain size, surface roughness, photo‐response, carrier lifetime, and contact potential difference of absorbers. Cs‐(FAPbI₃)_0.85(MAPbBr₃)_0.15 absorbers also present superior charge transport, as well as reduced carrier recombination and decreased trap densities via DMSO‐molecule‐control, enabling performance improvement on both long‐term stability and photovoltaic parameters of 1 cm² PSCs. Champion planar cells demonstrated a power conversion efficiency (PCE) of 21.07% (0.159 cm²) and PCE of 19.4% (1 cm²) with negligible hysteresis. Moreover, 1 cm² devices retained 90% of initial PCE after aging 50 days in ambient air.

Transparent conducting electrodes based on modified high‐conductivity PEDOT:PSS on 100 µm‐thick flexible glass substrates with a sheet resistance of ≈30 Ω/sq and a broad transmission window between 300 and 800 nm enable organic solar cells with a power conversion efficiency of 8.0%, which is higher than devices comprising ITO or PEDOT:PSS anodes on plastic substrates.

The ability for organic solar cells to be conformable and bendable enables them to be used in a broad range of applications. Indium tin oxide (ITO) or PEDOT:PSS on plastic substrates such as poly(ethylene terephthalate) or poly(ethylene napthalate) (PET or PEN) have been used for transparent conductive electrodes (TCEs) for flexible devices. However, ITO is brittle and when used on flexible substrates is prone to cracking, and the acidity of PEDOT:PSS can lead to corrosion of the ester‐based plastic substrates and cause device degradation. In this work, TCEs based on modified high‐conductivity PEDOT:PSS on 100 μm‐thick flexible glass substrates are used as the anode for organic solar cells. The optimized PEDOT:PSS TCE anode on flexible glass has a sheet resistance of ≈30 Ω/sq and a transmission of ≈77% at 550 nm, with a broad transmission window between 300 and 800 nm. The best PEDOT:PSS on flexible glass‐based organic solar cell has a power conversion efficiency (PCE) of 8.0%, which is higher than devices comprising ITO or PEDOT:PSS on PEN, which have PCEs of 6.4% and 5.8%, respectively. It is also found that the ultra‐thin glass devices can be scaled, with 1.6 cm² flexible cells having an efficiency of 5.2%.

Solution‐processed layers of PEDOT:PSS and SnO₂ nanoparticles serve as an interconnecting layer (ICL) for solution‐processed tandem polymer solar cells in p‐i‐n and n‐i‐p configurations, providing power conversion efficiencies over 10%. The resilience of SnO₂ against acidic PEDOT:PSS dispersions enables fabricating p‐i‐n tandem cells with negligible loss in an open‐circuit voltage, giving it a distinct advantage compared to ubiquitously used ZnO.

Tin oxide nanoparticles are employed as an electron transporting layer in solution‐processed polymer solar cells. Tin oxide based devices yield excellent performance and can interchangeably be used in conventional and inverted device configurations. In combination with poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a hole transporting layer, tin oxide forms an effective interconnecting layer (ICL) for tandem solar cells. Conventional and inverted tandem cells with this ICL provide efficiencies up to 10.4% in good agreement with optical‐electrical modeling simulations. The critical advantage of tin oxide in an ICL in a conventional tandem structure over the commonly used zinc oxide is that the latter requires the use of a pH‐neutral formulation of PEDOT:PSS to fabricate the ICL, limiting the open‐circuit voltage (V _OC) because of its low work function. The SnO₂/PEDOT:PSS ICL, on the other hand, provides a nearly loss‐free V _OC.

A fluorinated spiro[fluorene‐9,9′‐xanthene] based hole transport material (HTM), 2mF‐X59, is designed and synthesized within two steps for sensitive‐dopant‐free, high efficient, and stable perovskite solar cells (PSCs). 2mF‐X59 shows the lowered HOMO level, improved hole mobility and hydrophobicity, compared to its nonfluorinated counterpart X59. Without the use of any sensitive‐dopants, the optimized 2mF‐X59‐based PSCs exhibit a power conversion efficiency up to 18.13% with impressive long‐term stability.

Despite the substantial development of efficient hole transporting materials (HTMs) for high‐performance perovskite solar cells (PSCs), optimization of the HTMs to sensitive‐dopant‐free HTMs for high efficient PSCs with prominent stability have rarely been reported. Herein, a low‐cost fluorinated spiro[fluorene‐9,9′‐xanthene] based HTM termed 2mF‐X59 is designed and synthesized. In comparison with its reported nonfluorinated counterpart X59, 2mF‐X59 shows lowered highest occupied molecular orbital (HOMO) level, improved hole mobility, and hydrophobicity. Aided by 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) to further lower the HOMO level of 2mF‐X59 and improve its hole transfer, the optimized 2mF‐X59 based PSCs show a maximum power conversion efficiency (PCE) of 18.13% without the use of any sensitive‐dopants (e.g., lithium salt/4‐tert‐butylpyridine), which is comparable to the Spiro‐OMeTAD based PSCs (18.22%) with sensitive dopants. More importantly, the sensitive‐dopant‐free 2mF‐X59 based PSCs maintain 95% of their initial performance for more than 500 h under air exposure, showing much better long‐term stability than control PSCs based on Spiro‐OMeTAD with sensitive dopanst. This is the first case that a sensitive‐dopant‐free HTM is demonstrated in PSCs with a high PCE (>18%) and good stability by optimizing the literature HTM. This work could pave a new way to develop low‐cost sensitive‐dopant‐free HTMs for highly efficient and stable PSCs for practical applications.

The phase purity and vertical distribution The phase purity and vertical distribution of quasi‐2D perovskite is manipulated for their optoelectronic applications, which require different phase distributions. The direction of carrier transfer is tuned accordingly, proven by transient absorption spectroscopy. Solar cell performance is sensitive to the phase purity and dependent on vertical distribution as well.

Quasi two‐dimensional perovskites are promising alternatives to conventional three‐dimensional perovskites because of their high stability and easy tunability. However, controlling the phase distribution according to device architecture remains a major challenge. Here, the manipulation of phase purity and vertical distribution proven by ultrafast transient absorption spectroscopy, and their effect on device characteristics are reported. By adding ethyl acetate as antisolvent, the growth direction of the perovskite film is flipped. CH₃NH₃Cl and dimethyl sulfoxide are used to slow the growth rate of the crystal, which gives better phase purity. The direction of carrier transfer is tuned accordingly. It is found that solar cell performance is more sensitive to phase purity relative to vertical distribution. These findings are of importance for the applications of quasi‐2D perovskites in different types of devices that require to change phase purity and vertical distribution.

CZTS quantum dots are employed as hole transporting materials for CsPbBr₃ inorganic perovskite solar cells. More effective hole extraction and transfer properties, as well as stability have been demonstrated after introducing CZTS as the hole selective contact. This work reveals the great promise of CZTS as hole acceptors within inorganic perovskite‐based devices.

All‐inorganic CsPbBr₃ perovskite solar cells (PSCs) have recently generated tremendous interest in next‐generation cost‐effective and stable photovoltaic devices. However, the commonly used costly and unstable organic hole transporting material (HTM) has so far prevented the further development and large‐scale application of PSCs. In this work, Cu₂ZnSnS₄ quantum dots (CZTS QDs) are exploited as a novel inorganic HTM for CsPbBr₃ PSCs. Due to the well‐matched energy levels with the inorganic perovskite layer, a decent power conversion efficiency of 4.84% is achieved, which is quite comparable to the efficiency of the traditional device based on spiro‐OMeTAD HTM (5.36%). Moreover, the photoluminescence (PL) and impedance spectroscopy further demonstrate the more effective hole extraction and transfer properties of the CZTS QDs interface layer, making it a promising material for fabricating efficient and stable PSCs toward practical applications.

Perovskite solar cells contain various defects within the perovskite absorber and the corresponding interfaces, affecting device performance and stability. Fortunately, there have been tremendous efforts in advancing passivation techniques contributing to high‐efficiency devices with improved stability. Here, the state‐of‐the‐art passivation approaches for each layer of the perovskite cell with the aim of improving carrier extraction, reducing carrier recombination and improving cell stability and performance are reviewed.

Perovskite solar cells contain various defects within the perovskite absorber and the corresponding interfaces, affecting device performance and stability. Fortunately, there have been tremendous efforts in advancing passivation techniques contributing to high‐efficiency perovskite solar cell with improved stability. Here, the state‐of‐the‐art passivation approaches for each layer of the perovskite cell with the aim of improving carrier extraction, reducing carrier recombination, and/or improving cell stability are reviewed. Passivation of the electron transport layer can improve the stability of perovskite solar cells by reducing trap states or by physically separating the transport layer from contacting perovskite. Controlling the amount of PbI₂ in the perovskite precursor has been found to be effective in passivating defect states at the grain boundaries and on the surface. Additives such as elemental iodine, organic surfactants, and Group 1 metal compounds incorporated in perovskite precursors have been reported to passivate recombination trap centers. These approaches have also contributed to improved energy band alignment between carrier transport layers and perovskite absorber improving device performance. An effective strategy to improve moisture stability is the use of 2D perovskites or hydrophobic large cation molecules forming 2D or quasi‐2D phases at grain boundaries or film surfaces providing passivation and preventing moisture ingress.

Alkyl‐amine bound organolead halides are soluble in chlorobenzene. This finding prompts the authors to prepare perovskite precursor solutions using this nonpolar solvent and produce perovskite devices from conventionally layered to specially designed structures with consecutive (CH₃NH₃)PbI₃/(C₄H₉NH₃)₂PbI₄ double layers or PTAA@(CH₃NH₃)PbI₃ blend layers. This study is the first to use a nonpolar solvent for perovskite material processing, device fabrication, and architecture design.

Chlorobenzene (CB), which has been used as an anti‐solvent, is demonstrated here as a processing solvent for the fabrication of perovskite films and solar cells. This approach results from the unexpected finding that butylamine‐bound organolead iodides can be dissolved in CB to form precursor solutions. Together with previously established perovskite composition transformation methods, not only conventionally structured perovskite solar cells (PSCs) with a (CH₃NH₃)PbI₃ active layer but also nonconventionally structured devices with a consecutive (CH₃NH₃)PbI₃/(C₄H₉NH₃)₂PbI₄ double layer or a mixed poly(triaryl amine) (PTAA) and (CH₃NH₃)PbI₃ bulk heterojunction layer are successfully prepared and demonstrated with an optimal efficiency of 16.44%. This is the first time that nonpolar solvents are used for perovskite material processing, which can remove the solvent limitation and open a new avenue for designing and preparing perovskite devices with desired structures.

The series resistance of perovskite solar cells at their maximum power point is measured using the J_sc–V_oc technique. This technique also probes the limiting fill factor of the perovskite solar cell if the device was resistance‐free. Further investigation reveals that PTAA is an effective hole‐selective contact (capable of sustaining a high V_oc ) but is resistive to the holes it collects.

The fill factor (FF) of perovskite solar cells is considerably lower than that of gallium arsenide and silicon cells, though they have similar open‐circuit voltage deficits. To probe the FF loss, which mainly comes from series resistance, the J_sc –V_oc characterization technique is applied to perovskite solar cells. A continuous‐lamp solar simulator with an array of neutral density filters is used instead of the quasi‐steady‐state photoconductance technique commonly employed for silicon cells, which allows us to tune sweep parameters to accommodate the complex behavior of perovskites such as hysteresis. It is found that, for Cs_0.25FA_0.75Pb(Br_0.2I_0.8)₃ (CsFA) perovskite cells, sweeping from positive to negative voltage yields the same series resistance regardless of sweep speed, whereas this is not the case if the sweep is reversed. However, for CH₃NH₃PbI₃ perovskite cells, the series resistance is independent of the sweep speed in both sweep directions. It is also found that, for a poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA) hole contact, increasing the PTAA thickness barely changes the recombination‐limited pseudo‐FF, but reduces the FF due to increased series resistance. A maximum FF of 80.9% was achieved with the PTAA hole contact on a CsFA perovskite absorber.

A novel phenyl substituted benzo(1,2‐b:4,5‐b’)dithiophene (BDT) derivative containing both fluorine and sulfur atoms is designed and synthesized. A power conversion efficiency of 13.91% is achieved with a high open‐circuit voltage of 1.01 V, and a large short‐circuit current density of 18.51 mA cm⁻². The result demonstrates that PBTA‐PSF is a promising candidate for high‐performance donor polymers.

A novel phenyl substituted benzo(1,2‐b:4,5‐b’)dithiophene (BDT) derivative containing both fluorine and sulfur atoms is designed and synthesized. Furthermore, a wide bandgap polymer PBTA‐PSF based on the derivative shows a low highest occupied molecular orbital energy level and slightly reduces the donor materials’ optical bandgap, which has a complementary absorption with a narrow‐bandgap n‐type small molecule ITIC. As a result, a power conversion efficiency of 13.91% is achieved with a high open‐circuit voltage of 1.01 V, and a large short‐circuit current density of 18.51 mA cm⁻². The result demonstrates that PBTA‐PSF is a promising candidate for high‐performance donor and phenyl‐containing BDT derivatives and has potential in the design of high‐performance polymers for organic photovoltaics.

Owing to the facile method of Al addition, the conductivity, electron mobility, and band alignment at the SnO₂/perovskite interface have been dramatically improved. Besides, better surface coverage of SnO₂ films and lower defect density of the perovskite film are obtained. Benefiting from these advantages, the devices based on the Al: SnO₂ film exhibit a significant improvement in power conversion efficiency.

Owing to its splendid electrical and optical properties, tin oxide (SnO₂) has been proven to be an effective electron transport layer (ETL) material for high‐efficiency perovskite solar cells (PSCs). However, the surface coverage, conductivity, and energy loss at the SnO₂/perovskite interface still have room for improvement. Herein, a facile method by mixing a SnO₂ QD solution with an aluminum (Al) chloride precursor solution at room temperature to achieve the addition of Al into the SnO₂ QD (Al: SnO₂) precursor is proposed. Based on this strategy, conductivity, electron mobility, and band alignment with the perovskite layer have been significantly improved. Besides, the introduction of Al also increases the coverage of the SnO₂ film, consequently contribute to improving the capability to block the charge transfer from FTO to the ETL. Furthermore, fewer defect states are also demonstrated for the perovskite films deposited on Al: SnO₂ films than the control samples. With the optimized addition ratio of 5%, the devices exhibit an average efficiency (PCE) of 17.01%, which is superior to that of the control device of 15.80%. The champion device using Al: SnO₂ ETL delivers an impressive PCE of 18.20%. This research indicates that the low‐temperature solution‐processed Al: SnO₂ is a promising ETL for high‐efficiency PSCs.

It has been discovered that the existence of a potassium‐rich phase on the surface of 3D perovskite crystals passivates the grain boundaries, which can dramatically suppress the trap states as well as enhance dielectric confinement.

Recently, considerable researches have reported that the incorporation of potassium cation (K⁺) in lead halide perovskites obviously improves the performance of perovskite solar cells. The recent finding indicates that the interstitial occupancy position of K⁺ in perovskite lattice can increase ion‐migration barrier, which dramatically suppresses the hysteresis of the device. However, the enhancement of photoluminescence (PL) as well as bandgap variation cannot be interpreted by K⁺ interstitial state in perovskite. Considering this discrepancy, it has been found out that potassium‐rich phase grows in three dimensional (3D) perovskite crystal grain boundary through both experiments and theoretical simulations, which can efficiently passivate the grain boundaries on the 3D crystal surface and decrease trap states. Meanwhile, the dielectric confinement effect between potassium‐rich phase and 3D perovskite crystal, contributing to improvement of radiative recombination in perovskite absorber, can further support the enhancement and red‐shift of photoluminescence (PL) spectrum. Therefore, a power conversion efficiency of 20.4% has been achieved in K⁺ doped halide perovskite solar cell, and still maintains 90% initial efficiency after stored in 30% humidity at room temperature for 1000 h. These findings offer a new path for the structural manipulation by incorporating multi cations in perovskite materials.

A dithienobenzodithiophene‐based π‐conjugated polymer with fluorinated benzotriazole is applied through an anti‐solvent process to passivate the defects of the perovskite film. The fluorinated polymer interacts with undercoordinated Pb²⁺ ions to form a Pb‐F bond in the perovskite crystals, resulting in a reduced trap density, fast charge transfer, and enhanced performance and stability of the perovskite solar cell.

A dithienobenzodithiophene‐based π‐conjugated polymer consisting of fluorinated benzotriazole and benzothiadiazole is successfully applied through anti‐solvent method to passivate the defects of perovskite crystals. The fluorinated polymer interacts with under coordinated Pb²⁺ ions in the perovskite crystals to form Pb‐F bond which effectively passivates the defects. The trap density is reduced and the charge carrier transfer between the perovskite film and Spiro‐OMeTAD is also improved after passivation with the polymer. As a result, a power conversion efficiency (PCE) of 18.03% is achieved in the champion cell. After storing in an ambient environment with 60% relative humidity for 1000 h, the device still retains 90% of the original PCE. These results demonstrate that dithienobenzodithiophene‐based π‐conjugated polymers are promising materials for passivation of perovskite films to further improve the performance and stability of perovskite solar cells.

A near‐infrared non‐fullerene acceptor BTTIC is well compatible with different bandgap polymers, i.e., J71 (1.92 eV), PBDB‐T (1.80 eV), and PTB7‐Th (1.58 eV), which achieves power conversion efficiencies (PCEs) as high as 12.8%, 13.2%, and 10.4%, with fill factors all over 70%, suggesting BTTIC is a promising non‐fullerene acceptor for polymers selectivity.

Owing to their good polymer compatibility, fullerene derivatives, such as PC₆₁BM and PC₇₁BM, have been the dominant electron acceptors to pair with various polymer donors in polymer solar cells (PSCs). The recent surge of non‐fullerene materials leads to several high‐performance molecular acceptors. Despite their high performance in a given polymer/acceptor system, the generality of these acceptors, i.e., their compatibility with different donor polymers remains uncertain. Here, a high‐performance small molecule acceptor (SMA), BTTIC, is designed and synthesized to combine with three polymers with different bandgaps, namely J71 (1.92 eV), PBDB‐T (1.80 eV), and PTB7‐Th (1.58 eV). Complementary absorption, compatible energy levels, and particularly the favorable morphologies between BTTIC and the three polymers enable high power conversion efficiencies (PCEs), which are 12.8%, 13.2%, and 10.4% for J71:BTTIC‐, PBDB‐T:BTTIC‐, and PTB7‐Th:BTTIC‐based PSCs, respectively, significantly higher than the PCEs of the fullerene‐ or other non‐fullerene‐based counterparts. Moreover, another famous p‐type polymer donor PffBT4T‐2OD, which shows poor solubility in chloroform and has not yet been studied in non‐fullerene PSCs, is also investigated. Processing by dissolving PffBT4T‐2OD and BTTIC in boiling chloroform enables PffBT4T‐2OD:BTTIC‐based PSCs with a PCE of 10.18%, which is significantly higher than that of PSCs (4.78%) before using boiling chloroform processing. The good compatibility of BTTIC with polymers that have either large, moderate, or small bandgaps makes it a promising non‐fullerene acceptor for next‐generation non‐fullerene PSCs.

Nickel oxide based perovskite solar cells are reviewed comprehensively in the present paper. Particularly, the fabrication method for NiO _x films, surface modification, and doping strategies are discussed in detail with special attention paid to the relationship between the optoelectronic properties of NiO _x films and the performance of resulting perovskite solar cell devices.

Organic–inorganic halide perovskite solar cells (PSCs) have achieved great success in recent years with a demonstrated power conversion efficiency (PCE) increasing rapidly from 3.8% to 22.3% for single junction devices. Most high‐performance PSCs consist of a perovskite absorber sandwiched between an electron transport layer (ETL) and a hole transport layer (HTL), which extracts electrons (holes) and blocks holes (electrons) from the absorber efficiently. Inorganic hole transport materials have extracted extensive attention due to their higher mobility and better stability. Particularly, the excellent hole selective transport property of nickel oxide (NiO _x ) has been highlighted by its recent application in organometallic halide PSCs, due to the favorable band alignment formed between the halide perovskite absorber and NiO _x HTL. This comprehensive review summarizes the recent progress in the fabrication of NiO _x films and their application in PSCs. Special attention is paid to the optoelectronic properties of NiO _x films, which strongly depend on the synthesis methods and post‐treatment conditions, as well as the resulting photovoltaic device performance. Surface modification and doping strategies that are used to improve the optoelectronic properties of NiO _x films and the resulting device performance are discussed with emphasis. Finally, a short perspective of NiO _x ‐based PSCs is also provided.

Passivation

Moisture penetration through surface defects into the active layer is responsible for degradation of device performance in humid environments. In article no. 1800327, Zhijie Wang, Huiqiong Zhou, Shengchun Qu, and coworkers show that the interaction of the perovskite material with DRCN5T increases the durability of the device in ambient conditions, because the passivated defect sites on the film surface suppresses the transit of moisture or oxygen through the defects.

A sequential slot‐die (SSD) coating technique can lead the polymer to form pre‐aggregates, resulting in enhanced crystallinity and face‐on orientation which is superior for charge transport. As a result, large area (1 cm²) flexible devices with a power conversion efficiency of 7.11% are obtained. Therefore this approach offers a new strategy for the fabrication of large area flexible organic solar cells.

For the preparation of flexible organic solar cells (OSCs), the Roll‐to‐Roll slot‐die coating technique is preferable. Herein, a sequential slot‐die (SSD) coating strategy to fabricate flexible OSCs using non halogenated solvent under ambient atmosphere, is developed. The coating order of the active layer materials shows great influence on the performance of OSCs. It is found that, compared with the one‐step coating, the power conversion efficiency (PCE) of devices with an area of 0.75 cm², and fabricated by SSD coating process with the polymer as the first layer, is enhanced from 4.86 to 5.51% for the binary system, whereas from 6.09 to 7.32% for the ternary system, showing an increase of 13 and 20% in PCE, respectively. For the devices with a standard small area of 4 mm² and large area of 1 cm², PCE as high as 9.36 and 7.11% are obtained, respectively, which are among the top value for flexible devices fabricated by slot‐die coating. It turns out that the SSD coating process with the polymer as the first layer assists pre‐aggregation of the polymer to form better crystal domains with face‐on orientation. Therefore, a sequential deposition strategy could provide a new means for manufacturing the high efficiency flexible OSCs.

An intriguing maze‐like CH₃NH₃PbI₃ film featuring a bilayer structure with a dense bottom layer and a porous top layer is judiciously designed for electron transport layer‐free perovskite solar cells (PSCs). Such maze‐like perovskite film shows high crystallinity, superior light‐harvesting capability, and enables facilitated hole extraction at the perovskite/hole transport layer interface, thus leading to a PCE of 18.5% with negligible hysteresis.

Perovskite solar cells (PSCs) without an electron transport layer (ETL) exhibit fascinating advantages such as simplified configuration, low cost, and facile fabrication process. However, the performance of ETL‐free PSCs has been hampered by severe charge carrier recombination induced either by current leakage (insufficient perovskite film coverage) or inferior charge extraction. Herein, an additive‐assisted morphological engineering strategy is used to construct an intriguing bilayer perovskite film featuring a dense bottom layer and a maze‐like top layer. Such maze‐like perovskite films enable the construction of ETL‐free PSCs with a PCE of 18.5% and negligible hysteresis, which can be attributed to the higher crystallinity and superior light‐harvesting capability of the resultant perovskite film, as well as facilitated hole extraction at the hole transport layer (HTL)/perovskite interface. This work provides a simple approach to modify the perovskite film morphology and demonstrates the correlation between facilitated charge‐carrier extraction and high‐performance ETL‐free perovskite photovoltaics.

High‐quality perovskite films are fabricated via in situ substrate‐heating‐assisted deposition in air. The in situ substrate temperature significantly influences the morphology, composition, and band gap of resulted perovskite films. The perovskite solar cells fabricated in air show the efficiency up to 18.38%. The fabrication process and device structure offer the advantages of well matching with low‐cost, large‐scale printing techniques.

It is a great challenge to process highly efficient perovskite solar cells (PSCs) under ambient conditions, which limits their potential commercialization. Herein, high‐quality triple cation mixtures Cs_0.21FA_0.56MA_0.23(I_0.98Br_0.02)₃ perovskite films are fabricated through two‐step solution processes via in situ substrate‐heating‐assisted deposition under ambient conditions with a relative humidity of about 40%. The in situ substrate temperature during the deposition significantly influences the grain size and compactness of lead iodide films, and therefore greatly affects the morphology, composition, and band gap of resulted perovskite films. Based on the optimization of substrate temperature and the thickness of perovskite layer, PSCs with a planar heterojunction configuration of ITO/SnO₂/perovskite/Spiro‐OMeTAD/Ag are fabricated, which deliver a power conversion efficiency up to 18.38%. These results suggest that high‐performance PSCs can be fabricated under ambient conditions instead of an inert environment, providing a fundamental step for accelerating PSC commercialization.

Foldable paper‐based perovskite solar cells (PSCs) with high power conversion efficiency of 13.19% and robust foldability are demonstrated. Beneficial from ultrathin cellophane substrates combined with foldable TiO₂/ultrathin Ag/TiO₂ electrodes, the solar cells exhibit 50 single folding stability at full angle range from −180° to 180° and 10 dual folding stability, enabling size compactness and shape transformation of paper‐based PSCs.

Foldable paper‐based solar cells are attractive power sources for wearable and portable applications. Currently, low power conversion efficiency (PCE) and degradation under different folding conditions restrict practical applications of paper‐based solar cells. Herein are constructed solar cells on cellophane paper using oxide/ultrathin Ag/oxide (OMO) and perovskite as electrodes and absorbers, respectively. The perovskite solar cell (PSC) on cellophane exhibits a PCE of 13.19%, the highest among all the paper‐based solar cells. More importantly, beneficial from ultrathin cellophane substrates combined with foldable OMO electrodes, PSCs on paper exhibit 50 single folding and 10 dual folding stability: they preserve 85.3 and 84.1% of the initial PCE after −180° and +180° single folding for 50 cycles, respectively; and they remain 67.2 and 55.3% of the initial PCE after 10 inner and outer dual folding cycles, respectively. Furthermore, the solar cells after dual folding show serious cracks and delamination, leading to faster degradation than single folding. The highly efficient, foldable, and lightweight PSCs on cellophane are promising for future self‐powered paper‐based electronic applications.

Environmentally friendly 2,2,2‐trifluoroethylamine hydrochloride (TFEACl) is used in synergy with SnF₂ to enhance the efficiency and stability of FASnI₃‐based solar cells, due to the improvements in film quality, suppression of the Sn²⁺ oxidation and more favorable energy band alignment.

The environmentally friendly additive 2,2,2‐trifluoroethylamine hydrochloride (TFEACl) is used in synergy with SnF₂ to enhance the efficiency and stability of FASnI₃‐based solar cells. Both TFEA⁺ and Cl⁻ are present in the films, but only Cl⁻ is incorporated into the crystal lattice of the perovskite. The addition of TFEACl suppresses the segregation of SnF₂, resulting in improvements in film morphology, in addition to a more favorable energy band alignment, and improved suppression of the formation of Sn⁴⁺. Consequently, reduced charge recombination and improved charge collection result in an efficiency enhancement from 3.63 to 5.30%. The stability of the devices is also significantly enhanced, with devices with TFEACl retaining over 60% of initial PCE after 350 h of light soaking in ambient, while devices without TFEACl experience failure in 120 h under the same testing condition.

Precise amount of DRCN5T incorporation into perovskite precursors could effectively passivate the defect states on the surface, which results in improved the life time and mobility of carriers. An impressive PCE of 20.60% is realized with lower hysteresis and high stability under ambient conditions (RH 50–60%).

The additive engineering to hybrid organic‐inorganic perovskite precursors is an effective technique toward highly efficient stable photovoltaic devices, however, there is still a deficiency in fundamental understanding on how these additives affect the perovskite film and device performance as well. Herein is introduced a small organic molecule, DRCN5T, into a double‐cation perovskite precursor and the function on device performance is systematically investigated. An appropriate amount of DRCN5T into the precursor can promote the crystallization of film with successful suppression of δ‐FAPbI₃ phase, reduce grain boundaries and adequately passivate the native defect sites. In addition, the incorporation of DRCN5T also regulates the energy level alignment of the perovskite to charge transport layer suitably. This leads to the promotion of charge transport, reduction in non‐radiative recombination, and boosts the efficiency to a value of 20.60% with greatly reduced hysteresis in the device. Moreover, the treatment by DRCN5T also significantly increases the stability of the devices in ambient environment. These findings open the gate to produce highly crystallized perovskite/organic‐molecule active layers toward commercialization of perovskite solar cells.

The reduction and/or the fluorination of the TT‐units of the PBDTT‐TT polymers have crucial effects on the photostability of their polymer:fullerene solar cells. Reduction improves the photostability of the solar cells while fluorination destabilizes the photostability.

Polymer solar cells have a promising future for applications in our day to day usage of energy in small appliances and portable devices. However, their performance in terms of efficiency is limited by a number of factors, among which is their low open circuit voltage (V _oc). It is, therefore, understandable that much effort is channeled by the scientific community in improving the V _oc. One way to achieve this goal is the development of novel materials, for example, polymers, through chemical structure modification. Typical examples are addition (chlorination, fluorination, or sulfonylation) and/or reduction (from alkyl‐ester to ketone substituents) mechanisms. This paper reports on the study of the effect of these structural changes for V _oc enhancement on the performance of the polymers in polymer:fullerene solar cells. In particular, it looks at seven polymers of the polybenzodithiophene‐thienothiophene family, identifying the structural changes in the thienothiophene units or their moieties as a function of V _oc behavior in relation to their UV‐stability. The findings reveal that the fluorination of the TT‐units or having alkyl‐ester groups as substituents on the TT‐units is bad for photostability. However, when these alkyl‐ester groups are reduced into ketone substituents, the photostability behavior improves.

A new methodology is presented for preparing a dopant‐free Spiro‐OMeTAD film by dynamic spin‐coating the pristine Spiro‐OMeTAD solution from a halogen‐free green solvent THF, which yields a record efficiency of 17% as along with negligible hysteresis in planar PSCs. Importantly, the strategy brings the field a step closer toward cost‐effective and environmental friendly production of PSCs with enhanced longevity.

In this paper, highly efficient (17%) perovskite solar cells (PSCs) based on a hole‐transporting layer (HTL) made of dopant‐free Spiro‐OMeTAD processed from a non‐halogenated solvent (THF) are reported for the first time. In addition to the high efficiency, a negligible hysteresis effect is observed for the devices with dopant‐free Spiro‐OMeTAD hole‐transporting material (HTM), which is often a problem for planar n‐i‐p type PSCs. By eliminating the hydroscopic dopants, the ambient stability of the completed PSC devices are much improved. Another advantage of using THF as a solvent is that much less of the Spiro‐OMeTAD material is required (5 mg ml⁻¹) to coat the HTL compared to that used in a conventional chlorobenzene solvent (70 mg ml⁻¹). Our result provides a simple yet effective method to fabricate dopant‐free PSCs toward cost‐effective and environmental friendly production of PSCs with enhanced stability.

All‐bromide perovskite solar cells with gradient bandgap are constructed by vapor deposition procedure accompanying with the derivative‐phase to boost the hole extraction efficiency and stability. An impressive power conversion efficiency of 10.17% is obtained via a vapor deposition method for a hole transfer layer‐free inorganic PSC. The device also exhibits an excellent humidity and thermal stability for more than 3000 h in RH ≈45% environment and 700 h at 100 °C. These results pave a great advancement in all inorganic PSCs and also open the window of perovskite derivative‐phase.

Inorganic perovskite materials have demonstrated outstanding performance in the field of photovoltaic devices due to their superior charge carrier transport properties and excellent thermal stability. In particular, the inorganic perovskite derivative phases show special properties in terms of phase stability and optoelectronic application, especially in the phase transition investigation. However, their commercial applications still face challenges due to the large recombination at the interface, resulting in poor efficiency and metastable phases such as iodide perovskite existing in the film. Herein, an all‐bromide inorganic perovskite solar cell has been developed by introducing the derivative phases (CsPb₂Br₅ and Cs₄PbBr₆) to construct gradient bandgap architecture. This graded heterojunction device is realized with a controllable sequential vapor deposition procedure. The valance band maximum elevates gradually with the presence of derivative phases and effectively blocks electrons and boosts the hole extraction efficiency at the counter electrode, which promotes charge separation and reduces the interface recombination. Ultimately, an impressive power conversion efficiency of 10.17% is achieved through a CsPbBr₃/CsPbBr₃‐CsPb₂Br₅/CsPbBr₃‐Cs₄PbBr₆ architecture strategy with excellent stability above 3000 h (85% of initial performance) in a humid environment (@RH ≈45%) and 700 h (83% of initial efficiency) under thermal conditions (@ 100 °C).

A perovskite solar cell with both high efficiency and high thermal stability is examined. The optimized device achieved by engineering perovskite composition exhibits 92% power conversion efficiency retention in a stress test conducted at 85 °C/85% RH while exceeding 20% power conversion efficiency (certified efficiency of 20.8% at 1 cm²). These results reveal a great potential for future practical use.

Abstract

Perovskite solar cells have received great attention because of their rapid progress in efficiency, with a present certified highest efficiency of 23.3%. Achieving both high efficiency and high thermal stability is one of the biggest challenges currently limiting perovskite solar cells because devices displaying stability at high temperature frequently suffer from a marked decrease of efficiency. In this report, the relationship between perovskite composition and device thermal stability is examined. It is revealed that Rb can suppress the growth of PbI₂ even under PbI₂‐rich conditions and decreasing the Br ratio in the perovskite absorber layer can prevent the generation of unwanted RbBr‐based aggregations. The optimized device achieved by engineering perovskite composition exhibits 92% power conversion efficiency retention in a stress test conducted at 85 °C/85% relative humidity (RH) according to an international standard (IEC 61215) while exceeding 20% power conversion efficiency (certified efficiency of 20.8% at 1 cm²). These results reveal the great potential for the practical use of perovskite solar cells in the near future.

A synergistic effect is proposed by employing a dielectric mirror and a ternary strategy to precisely tune the color perception as well as semitransparent organic solar cell (ST‐OSC) performance. It results in the highest efficiency reported for neutral‐color ST‐OSCs to date.

Abstract

Neutral‐colored semitransparent organic solar cells (ST‐OSCs) have attracted considerable attention owing to their unique application in no‐visual‐obstacle building‐integrated photovoltaics. Toward this promising potential application, a synergistic effect is first proposed by employing a dielectric mirror and ternary photoactive layer with near‐infrared absorption to tune the color perception as well as ST‐OSC performance precisely. As a result, a neutral‐color ST‐OSC with high average transmittance of over 21% is successfully constructed, and a remarkable color‐rendering index approaching 100 and high power conversion efficiency (PCE) of 9.37% are simultaneously achieved. To the best of our knowledge, this is the highest PCE reported for neutral‐color ST‐OSCs to date. Importantly, this synergistic effect is demonstrated to be a universal strategy that is not only suitable for various photoactive layer systems, but can also be implanted in flexible substrate. The resulting neutral‐color flexible ST‐OSCs also show a promising PCE of 8.76%.

2D homochiral lead iodide perovskite ferroelectrics, [R‐ and S‐1‐(4‐chlorophenyl)ethylammonium]₂PbI₄, crystallize in a polar space group P1 at room temperature, and undergo a 422F1 type ferroelectric phase transition at 483 and 473.2 K, respectively, showing a multiaxial ferroelectric nature. However, their racemic counterpart adopts a centrosymmetric space group P2₁/c, exhibiting no high‐temperature phase transition.

Abstract

2D organic–inorganic lead iodide perovskites have recently received tremendous attention as promising light absorbers for solar cells, due to their excellent optoelectronic properties, structural tunability, and environmental stability. However, although great efforts have been made, no 2D lead iodide perovskites have been discovered as ferroelectrics, in which the ferroelectricity may improve the photovoltaic performance. Here, by incorporating homochiral cations, 2D lead iodide perovskite ferroelectrics [R‐1‐(4‐chlorophenyl)ethylammonium]₂PbI₄ and [S‐1‐(4‐chlorophenyl)ethylammonium]₂PbI₄ are successfully obtained. The vibrational circular dichroism spectra and crystal structural analysis reveal their homochirality. They both crystalize in a polar space group P1 at room temperature, and undergo a 422F1 type ferroelectric phase transition with transition temperature as high as 483 and 473.2 K, respectively, showing a multiaxial ferroelectric nature. They also possess semiconductor characteristics with a direct bandgap of 2.34 eV. Nevertheless, their racemic analogue adopts a centrosymmetric space group P2₁/c at room temperature, exhibiting no high‐temperature phase transition. The homochirality in 2D lead iodide perovskites facilitates crystallization in polar space groups. This finding indicates an effective way to design high‐performance 2D lead iodide perovskite ferroelectrics with great application prospects.

The molecular orientation and charge extraction of PEDOT:PSS‐based hole‐transporting layers are effectively modulated through fine tuning of the surface energy by introducing poly(styrene sulfonic acid) sodium salts or nickel formate dihydrate, which boosts the fill factor and eventual efficiency of organic solar cells based on fullerene and nonfullerene acceptors.

Abstract

Interface properties are of critical importance for high‐performance bulk‐heterojunction (BHJ) organic solar cells (OSCs). Here, a universal interface approach to tune the surface free energy (γ_S) of hole‐transporting layers (HTLs) in a wide range through introducing poly(styrene sulfonic acid) sodium salts or nickel formate dihydrate into poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is reported. Based on the optimal γ_S of HTLs and thus improved face‐on molecular ordering in BHJs, enhanced fill factor and power conversion efficiencies in both fullerene and nonfullerene OSCs are achieved, which is attributed to the increased charge carrier mobility and sweepout with reduced recombination. It is found that the face‐on orientation‐preferred BHJs (PBDB‐TF:PC₇₁BM, PBDB‐T:PC₇₁BM, and PBDB‐TF:IT‐4F) favor HTLs with higher γ_S while the edge‐on orientation‐preferred BHJs (PDCDT:PC₇₁BM, P3HT:PC₇₁BM and PDCBT:ITIC) are partial to HTLs with lower γ_S. Based on the surface property–morphology–device performance correlations, a suggestion to select a suitable HTL in terms of γ_S for a specific BHJ with favored molecular arrangement is provided. This work enriches the fundamental understandings on the interface characteristics and morphological control toward high‐efficiency OSCs based on a wide range of BHJ materials.