Mahui

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).

Compared with polycrystalline films, grain‐boundary‐free perovskite single‐crystal films are expected to significantly boost the optoelectronic performance of devices because of their higher carrier mobility, longer diffusion length, and better stability. This review is intended to provide a timely overview of the preparation methods, inherent properties, and state‐of‐the‐art applications of perovskite single‐crystal thin films and offers an outlook for future research.

Metal‐halide perovskites have aroused intense interest in the scientific community by virtue of their numerous remarkable optoelectronic properties, which render them promising candidates for applications in various optoelectronic fields, such as solar cells, light‐emitting diodes, photodetectors, and lasers. Compared with perovskite polycrystalline films and nanocrystals, grain‐boundary‐free single‐crystal perovskites possess lower trap‐state densities, higher carrier mobilities, and longer diffusion lengths, which are supposed to deliver superior optoelectronic performance. However, the thickness (a few millimeters) of typical bulk single‐crystal perovskites are much greater than their carrier diffusion length (e.g., MAPbI₃ SC, ≈175 µm), which results in severe charge accumulation and significantly hinders their development. To this end, fabricating single‐crystal thin films is of great importance for further exploring the potential of single‐crystal perovskites in various applications. In this paper, the rapid and prosperous developments in the fabrication methods of perovskite single‐crystal thin films are systematically summarized and recent encouraging progress in their physical and chemical properties as well as the optoelectronic applications (solar cells, photodetectors, and light‐emitting diodes) of single‐crystal thin films are reviewed. Finally, the challenges and a brief outlook for further improving the quality of perovskite single‐crystal thin films and optimizing the device design are highlighted.

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.

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 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.

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 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.

A thin layer of polyethylene oxide (PEO) is introduced to modify the energy level alignment at the interface between an FA_0.8Cs_0.2PbI_2.64Br_0.36 perovskite and a carbon electrode. The PEO‐modified perovskite cell shows 22% increase in power conversion efficiency and enhanced stability keeping 77% of the initial value after being aged for 192 h under the conditions of 85 °C and 85% humidity without encapsulation.

Abstract

Perovskite solar cells (PSCs) have attracted great attention in the past few years due to their rapid increase in efficiency and low‐cost fabrication. However, instability against thermal stress and humidity is a big issue hindering their commercialization and practical applications. Here, by combining thermally stable formamidinium–cesium‐based perovskite and a moisture‐resistant carbon electrode, successful fabrication of stable PSCs is reported, which maintain on average 77% of the initial value after being aged for 192 h under conditions of 85 °C and 85% relative humidity (the “double 85” aging condition) without encapsulation. However, the mismatch of energy levels at the interface between the perovskite and the carbon electrode limits charge collection and leads to poor device performance. To address this issue, a thin‐layer of poly(ethylene oxide) (PEO) is introduced to achieve improved interfacial energy level alignment, which is verified by ultraviolet photoemission spectroscopy measurements. Indeed as a result, power conversion efficiency increases from 12.2% to 14.9% after suitable energy level modification by intentionally introducing a thin layer of PEO at the perovskite/carbon interface.

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, crystalize 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.

A thin layer of polyethylene oxide (PEO) is introduced to modify the energy level alignment at the interface between an FA_0.8Cs_0.2PbI_2.64Br_0.36 perovskite and a carbon electrode. The PEO‐modified perovskite cell shows 22% increase in power conversion efficiency and enhanced stability keeping 77% of the initial value after being aged for 192 h under the conditions of 85 °C and 85% humidity without encapsulation.

Abstract

Perovskite solar cells (PSCs) have attracted great attention in the past few years due to their rapid increase in efficiency and low‐cost fabrication. However, instability against thermal stress and humidity is a big issue hindering their commercialization and practical applications. Here, by combining thermally stable formamidinium–cesium‐based perovskite and a moisture‐resistant carbon electrode, successful fabrication of stable PSCs is reported, which maintain on average 77% of the initial value after being aged for 192 h under conditions of 85 °C and 85% relative humidity (the “double 85” aging condition) without encapsulation. However, the mismatch of energy levels at the interface between the perovskite and the carbon electrode limits charge collection and leads to poor device performance. To address this issue, a thin‐layer of poly(ethylene oxide) (PEO) is introduced to achieve improved interfacial energy level alignment, which is verified by ultraviolet photoemission spectroscopy measurements. Indeed as a result, power conversion efficiency increases from 12.2% to 14.9% after suitable energy level modification by intentionally introducing a thin layer of PEO at the perovskite/carbon interface.

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.

Three‐layer graphene is used as the transparent conducting electrode for flexible organic solar cells. A thick bulk heterojunction active layer comprised of a blend of the non‐polymeric molecular donor BQR and PC₇₁BM enables coverage of the rough graphene surface so as to avoid shorted devices. The best devices (PET/graphene/molybdenum oxide/BHJ/calcium/aluminum) have a photoconversion efficiency of 5.8%.

Solution processed flexible organic solar cells (OSCs) are of interest due to their potential use as environmentally friendly, shapeable, or wearable energy. Such flexible devices require compatible transparent conducting electrodes (TCEs). The use of three‐layer graphene as a useful TCE for flexible OSCs is reported. The conformal coating of the graphene‐based TCE with good retention of performance was achieved using a bulk heterojunction (BHJ) active layer comprised of the non‐polymeric molecular (5Z,5′Z)‐5,5′‐[(5‴,5‴‴′‐{4,8‐bis[5‐(2‐ethylhexyl)‐4‐n‐hexylthiophen‐2‐yl]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl}bis{3′,3″,3‴‐tri‐n‐hexyl‐[2,2′:5′,2″:5″,2‴‐quaterthiophene]‐5‴,5‐diyl})bis(methanylylidene)]bis[3‐n‐hexyl‐2‐thioxothiazolidin‐4‐one] (BQR) donor and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) as the acceptor. This material combination enables thick BHJ junctions to be used so that the roughness of the graphene surface did not lead to shorted devices. The best graphene/poly(ethylene terephthalate) (PET) devices (PET/graphene/molybdenum oxide/BHJ/calcium/aluminum) show a photoconversion efficiency (PCE) of 5.8%, which while excellent was lower than that of a similar device architecture that used ITO/glass as the anode. The power losses of the graphene/PET‐based cells mainly resulted from absorption losses caused by the optical profile distribution in the device and the relatively high sheet resistance of the anode, leading to an 18% decrease in the short‐circuit current and lower fill factor, respectively.

PBDFFPD possesses a facile synthetic route, presents a large conjugated plane, and depicts a deep HOMO energy level. These admirable properties generate a remarkable PCE of 9.58% with a large FF of 70.1% when solar cells are fabricated based on PBDFFPD:ITIC. Obviously, PBDFFPD accords with the PSCs design philosophy of low cost, is adaptable for the mass production of PSCs, and deserves further research.

Non‐fullerene polymer solar cells (NF‐PSCs) have achieved tremendous progress in power conversion efficiency (PCE), which is mainly attributed to the well absorption complementation and the admirable energy‐level alignment between donor polymers and fullerene‐free acceptors. However, the development of efficient donor polymers pairing with fullerene‐free acceptors relatively lags behind that of fullerene‐free acceptors in terms of number and diversity for fabricating NF‐PSCs. In this work, a two‐dimensional medium bandgap copolymer (PBDFFPD) based on benzo[1,2‐b:3,4‐b′]difuran (BDF) and furo[3,4‐c]pyrrole‐4,6‐dione (FPD), is firstly designed and synthesized. The as‐prepared polymer possesses a large conjugated plane with negligible torsion, strong intermolecular and intramolecular interaction, and deep highest occupied molecular orbital (HOMO) energy level. The optimized photovoltaic device based on PBDFFPD:ITIC wins a remarkable PCE of 9.58% with a large FF of 70.1%, the highest values ever reported for FPD‐based polymers. In addition, the statistical data from different batches of devices shows that PSCs based on PBDFFPD:ITIC at optimized conditions depict an excellent reproducibility of PCE with a deviation of 2.29%. The results demonstrate that PBDFFPD possesses great potential for constructing highly efficient NF‐PSCs.

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.

Halide lead perovskites for ionizing radiation detection

Halide lead perovskites for ionizing radiation detection, Published online: 06 March 2019; doi:10.1038/s41467-019-08981-w

Impacts of alkaline on the defects property and crystallization kinetics in perovskite solar cells

Impacts of alkaline on the defects property and crystallization kinetics in perovskite solar cells, Published online: 07 March 2019; doi:10.1038/s41467-019-09093-1

A novel method for defects passivation in perovskite solar cells via controlling the electron density distribution of D‐π‐A molecule is proposed. As the polarity of the passivated molecule increases, the passivation effect on the under‐coordinated Pb²⁺ defects will be more obvious, leading to an increase of 80 mV in the open circuit voltage of the devices.

Abstract

Organic–inorganic hybrid perovskite solar cells (PSCs) are a promising photovoltaic technology that has rapidly developed in recent years. Nevertheless, a large number of ionic defects within perovskite absorber can serve as non‐radiative recombination center to limit the performance of PSCs. Here, organic donor‐π‐acceptor (D‐π‐A) molecules with different electron density distributions are employed to efficiently passivate the defects in the perovskite films. The X‐ray photoelectron spectroscopy (XPS) analysis shows that the strong electron donating N,N‐dibutylaminophenyl unit in a molecule causes an increase in the electron density of the passivation site that is a carboxylate group, resulting in better binding with the defects of under‐coordinated Pb²⁺ cations. Carrier lifetime in the perovskite films measured by the time‐resolved photoluminescence spectrum is also prolonged by an increase in donation ability of the D‐π‐A molecules. As a consequence, these benefits contribute to an increase of 80 mV in the open circuit voltage of the devices, enabling a maximum power conversion efficiency (PCE) of 20.43%, in comparison with PCE of 18.52% for the control device. The authors' findings provide a novel strategy for efficient defect passivation in the perovskite solar cells based on controlling the electronic configuration of passivation molecules.