Mahui

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.

Three A₂‐A₁‐D‐A₁‐A₂ type small molecules are used as electron acceptors for fullerene‐free organic solar cells, and the cyano‐containing A₂ segments have a large effect on the open‐circuit voltage (V _OC) and power conversion efficiency (PCE). By utilizing the “same‐acceptor‐strategy” and chosing J71 as donor polymer, the dicyano containing molecule of BTA3 affords the highest PCE of 8.60% with a V _OC of 1.20 V.

To achieve efficient organic solar cells (OSCs), the design of promising non‐fullerene small molecular acceptors (SMAs) is crucially important and the relationship between the chemical structure and optoelectronic properties needs to be further investigated. Herein, an A₂‐A₁‐D‐A₁‐A₂ molecular skeleton is adopted to study the effect of end‐capped A₂ groups containing different numbers of cyano units, where D and A₁ are fixed as indacenodithiophene (IDT) and benzotriazole (BTA) units, respectively. Utilizing the “same‐acceptor‐strategy,” three BTA‐based SMAs, named as BTA701, BTA3, and BTA703, are paired with a BTA‐based p‐type polymer J71. The open‐circuit voltage (V _OC) gradually decreases with the enhancement of electron‐accepting ability of terminal A₂ units, from 1.32 V (BTA701) to 1.20 V (BTA3) and to 0.85 V (BTA703). The device J71:BTA3 eventually shows the best power conversion efficiency (PCE) of 8.60% with a V _OC up to 1.2 V because of the complementary light absorption, high and balanced hole and electron mobility, suitable phase separation, and crystallinity. This study indicates that appropriate cyano‐containing units in BTA‐based SMAs can effectively modulate the absorption, energy levels, charge mobility and surface free energy, which can provide valuable insights to the further design of SMAs. In addition, these results prove that the “same‐acceptor‐strategy” is simple and effective to realize a V _OC as high as 1.2V.

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).

Br induced room temperature crystallization of highly photoactive black phase FA‐based perovskite films with high performance and reproducibility is reported. The halide Br/I formulation are 0.2/2.8 and 0.5/2.5 for room‐temperature perovskite crystallization at 35–40 °C and 20–25 °C, yielding solar to electric conversion efficiency of 19.59 and 17.53% with high reproducibility, respectively.

State‐of‐the art perovskite solar cells (PSCs) are obtained by using a high‐crystalline and uniform morphological perovskite film that usually requires a thermal procedure to induce its crystallization. Room temperature processing photoactive perovskite film represents a feasible approach to break through the technology barrier arising from high temperature annealing procedures; however, the photovoltaic performance of fabricated PSCs varies significantly in most routine laboratories with ambient temperature altering. Herein, the authors report for the first time that highly photoactive black phase FA‐based perovskite films with high performance and reproducibility can be room temperature processed via the Br induced crystallization effect. It is found that Br adding content varies as a function of ambient temperature fluctuation from 35–40 to 20–25 °C. The halide Br/I formulation are 0.2/2.8 and 0.5/2.5 for room‐temperature perovskite crystallization in ambient temperatures of 35–40 and 20‐25 °C, yieldings solar to electric power conversion efficiency of 19.59 and 17.53% with high reproducibility, respectively. This efficiency (19.59%) is comparable to the best‐performing PSCs based on thermal processing perovskite films. This work provides a valuable and practical guide to room‐temperature fabrication of PSCs with high efficiency and reproducibility by delicate control of halide anions.

A strategy to prepare efficient carbon‐based CsPbI₂Br perovskite solar cells is explored by using Co₃O₄ nanomaterial as hole transport layer (HTM). It is found that the Co₃O₄ inorganic HTM effectively promotes photo‐generated charges separation and extraction, and suppress charge recombination at the CsPbI₂Br/carbon electrode interface, leading to the enhanced performance.

Carbon‐based perovskite solar cells (PSCs) have gathered much attention due to their excellent thermal stability and low cost. However, the typically used hole‐conductor‐free PSCs based on carbon electrodes show the worst performance due to the serious charge recombination at the perovskite/carbon interface. In this work, the efficient and stable carbon‐based CsPbI₂Br PSCs using Co₃O₄ as the hole transport material (HTM) are fabricated and their photoelectric properties are systematically investigated. It is found that the Co₃O₄ inorganic HTM effectively promotes photo‐generated charges separation and extraction, and suppresses charge recombination at the CsPbI₂Br/carbon electrode interface, resulting in the improved photovoltaic performance. At the optimal Co₃O₄ concentration, the carbon‐based CsPbI₂Br PSCs achieve the maximum efficiency of 11.21% with a negligible J–V hysteresis. This work provides a novel strategy to fabricate efficient and stable all‐inorganic PSCs.

Additive‐free all‐polymer solar cells (all‐PSCs) devices based on TTFQx‐T1:N2200 are fabricated and the active layer (TTFQx‐T1:N2200) processed with THF and CHCl₃. The optimized device processed with THF exhibited better photovoltaic properties than that processed with CHCl₃. This work afforded a feasible strategy for constructing high‐performance all‐PSCs via a simple eco‐friendly processing method.

In this work, a medium bandgap quinoxaline (Qx) based polymer, named TTFQx‐T1, and a narrow bandgap n‐type polymer, named N2200, are employed to fabricate all‐polymer solar cells (all‐PSCs), which exhibited good light absorption for high short circuit current density (J _sc), well‐matched molecular energy level for good charge separation and high open circuit voltage (V _oc). Chlorinated solvents are harmful to both the environment and human beings; therefore, it is important to develop environmentally friendly solvents. Considering this, the green solvent tetrahydrofuran (THF) was employed to process all‐PSCs. The blend films based on TTFQx‐T1:N2200 processed with THF and thermal annealing (TA) exhibited better phase separation and preferential face‐on orientation toward the substrate, which benefited the exciton dissociation and charge carrier mobilities for higher FF and J _sc. The optimized device based on TTFQx‐T1:N2200 delivered an efficient power conversion efficiency of 8.63%, which is the highest value for all‐PSCs from Qx based polymers.

In an inverted planar perovskite solar cell employing a hole transporting NiO thin film, photovoltaic performance is found to depend significantly on annealing atmosphere when preparing the NiO film. The best power conversion efficiency can be achieved from the NiO film annealed at the oxygen partial pressure of 30% in mixture of O₂ and N₂.

The effect of annealing atmosphere and importance of oxygen partial pressure upon annealing NiO film for achieving high efficiency inverted perovskite solar cells (PSCs) is reported. The solution‐process NiO films are deposited on an FTO (fluorine‐doped tin oxide) substrate and annealed at 400 °C under different atmospheres of air, O₂, N₂, and Ar. The devices using air‐ and O₂‐annealed NiO films show better photovoltaic performance than the N₂‐ and Ar‐annealed ones, mostly due to large difference in photocurrent density (J _sc) of ≈20 mA cm⁻² for air and O₂ vs ≈15 mA cm⁻² for N₂ and Ar. Oxygen‐excess condition leads to more p‐type characteristics along with better electrical and interfacial properties, leading to higher photovoltaic performance. When comparing air and O₂ condition, the air‐annealed NiO film shows slightly better power conversion efficiency (PCE) (15.68% for air vs. 14.93% for O₂), being indicative of importance of oxygen partial pressure. By carefully modifying oxygen content, the best photovoltaic performance is achieved from the NiO film annealed at the O₂/(O₂+N₂) ratio of 30%, delivering a PCE of 16.32%.

A facile and eco‐friendly approach is introduced to greatly promote the molecular order of nominally amorphous polymers and thus realize high‐efficiency in sequentially deposited (SD) nonfullerene solar cells. Applying a green solvent, (R)‐(+)‐limonene, enhances the polymer order and yields the best efficiency. Additionally, strong relationships between solvent, interaction parameter, and long period are observed for these new SD devices.

Abstract

Casting of a donor:acceptor bulk‐heterojunction structure from a single ink has been the predominant fabrication method of organic photovoltaics (OPVs). Despite the success of such bulk heterojunctions, the task ofcontrolling the microstructure in a single casting process has been arduous and alternative approaches are desired. To achieve OPVs with a desirable microstructure, a facile and eco‐compatible sequential deposition approach is demonstrated for polymer/small‐molecule pairs. Using a nominally amorphous polymer as the model material, the profound influence of casting solvent is shown on the molecular ordering of the film, and thus the device performance and mesoscale morphology of sequentially deposited OPVs can be tuned. Static and in situ X‐ray scattering indicate that applying (R)‐(+)‐limonene is able to greatly promote the molecular order of weakly crystalline polymers and form the largest domain spacing exclusively, which correlates well with the best efficiency of 12.5% in sequentially deposited devices. The sequentially cast device generally outperforms its control device based on traditional single‐ink bulk‐heterojunction structure. More crucially, a simple polymer:solvent interaction parameter χ is positively correlated with domain spacing in these sequentially deposited devices. These findings shed light on innovative approaches to rationally create environmentally friendly and highly efficient electronics.

3D chiral hybrid organic–inorganic perovskites are both kinetically and thermodynamically stable based on theoretical calculation, and chirality is transferred from chiral cations to the perovskite framework, which is of great interest in the fields of piezoelectricity, pyroelectricity, ferroelectricity, topological quantum engineering, circularly polarized optoelectronics, and spintronics.

Abstract

Hybrid organic–inorganic perovskites (HOIPs), in particular 3D HOIPs, have demonstrated remarkable properties, including ultralong charge‐carrier diffusion lengths, high dielectric constants, low trap densities, tunable absorption and emission wavelengths, strong spin–orbit coupling, and large Rashba splitting. These superior properties have generated intensive research interest in HOIPs for high‐performance optoelectronics and spintronics. Here, 3D hybrid organic–inorganic perovskites that implant chirality through introducing the chiral methylammonium cation are demonstrated. Based on structural optimization, phonon spectra, formation energy, and ab initio molecular dynamics simulations, it is found that the chirality of the chiral cations can be successfully transferred to the framework of 3D HOIPs, and the resulting 3D chiral HOIPs are both kinetically and thermodynamically stable. Combining chirality with the impressive optical, electrical, and spintronic properties of 3D perovskites, 3D chiral perovskites is of great interest in the fields of piezoelectricity, pyroelectricity, ferroelectricity, topological quantum engineering, circularly polarized optoelectronics, and spintronics.