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As one of the most widely used hole transport materials (HTMs) in optoelectronics devices, 2,2',7,7'‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9‐spirobifluorene (spiro‐OMeTAD) has endowed perovskite solar cells (PSCs) with record power conversion efficiencies (PCEs). However, the long oxidation time in the ambient atmosphere is time‐consuming. Furthermore, commonly used solvents for spiro‐OMeTAD film processing such as chlorobenzene (CB) are toxic, which severely hinders the commercialization of PSCs. Herein, ethyl acetate (EA) serves as a superior green solvent alternative to the typical processing solvent, which substantially reduces the oxidation time of spiro‐OMeTAD. Without postoxidation treatment and any other additional oxidizing agents, the resultant device delivers a high PCE of 23.3%, significantly outperforming the CB‐based device. It is also the highest efficiency obtained from nonhalogenated solvent‐processed spiro‐OMeTAD. The electrostatic potential mapping demonstrates that the electron density at nitrogen atoms of EA‐processed spiro‐OMeTAD is more delocalized, leading to a faster oxidation. Furthermore, the processing solvent EA is a green solvent with low toxicity, and the amount of HTMs used in the fabrication of solar cells can be dramatically reduced. This study provides a new solution for processing spiro‐OMeTAD, which is ideal for the mass production of PSCs. [ABSTRACT FROM AUTHOR]

Heterojunction perovskite solar cells combine the stability of 2D perovskites and the high efficiency of 3D perovskites, making them an excellent photovoltaic candidate. While heterojunctions with intermixed or gradient perovskites can reduce surface recombination, the aggregation and phase distribution of 2D perovskite induce transport losses, thereby limiting device fill factors. Accordingly, a bulk in situ reconstruction (BISR) strategy is proposed to induce the reconstruction of 3D perovskites on a minim self‐assembled 2D crystal seed, forming heterojunction perovskite that runs through the entire active layer. This facilitates charge extraction, relieves tensile stress, and avoids the decomposition of perovskite on grain boundaries. As a result, the best‐performing heterojunction perovskite solar cells show a high‐power conversion efficiency (PCE) of 24.06% with 82.9% FF for the small‐area device (0.105 cm2) and a superior PCE of 19.2% for the large‐area module (5 × 5 cm2). Importantly, the unencapsulated device shows dramatically improved operational stability, maintaining 87% of its initial efficiency after 8000 h of storage under ambient atmosphere at room temperature. This work provides an effective and simple approach to establish heterojunction perovskite to simultaneously boost the efficiency and stability of PSCs. [ABSTRACT FROM AUTHOR]

Organic‐inorganic lead halide perovskite are promising photovoltaic materials, but their intrinsic defects and crystalline quality severely deteriorate the solar cells efficiency and stability. Herein, potassium 1,1,2,2,3,3‐hexafluoroprop‐ane‐1,3‐disulfonimide (KHFDF) is introduced into PbI2 precursor solution to passivate various defects and improve the crystalline quality of perovskite films. It is found that KHFDF can inhibit PbI2 crystallization, thus tuning the crystal orientation and growth of perovskite films. Furthermore, KHFDF with dual‐functional sulfonyl group cannot only passivate grain boundaries (GBs), but also passivate the defects at GBs via strong interaction with undercoordinated Pb2+ and/or hydrogen bonding with FA+, while the K+ counter cations allow ionic interaction with undercoordinated I−. As a result, the KHFDF‐modified films exhibit high quality with a larger grain size and a reduced trap‐state density, thereby suppressing the trap‐state nonradiative recombination. And the devices show a champion efficiency up to 24.15%, benefiting from a sharp enhancement of open‐circuit voltage (Voc) of 1.183 V and fill factor of 81.78%. In addition, due to the enhanced humidity tolerance and chemical structure stability, the devices exhibit excellent long‐term humidity and thermal stability without encapsulation. [ABSTRACT FROM AUTHOR]

The outstanding optoelectronic properties of metal halide perovskites make them an attractive photovoltaic absorber material and has rapidly culminated in the development of highly efficient perovskite solar cells outperforming many conventional alternatives. However, the device stack still suffers from non‐negligible losses induced by various nonradiative recombination processes, which are not fully understood till date. This paper highlights recent findings attempting to understand the nature and origin of nonradiative recombination induced losses within the device stack, as well as the quantification of the magnitude and rates associated with key loss pathways mostly via steady state and transient contactless optical techniques. These studies show that nonradiative recombination processes occurring at interfaces are more dominant than those within the bulk of the perovskite absorber. However, recent findings also show that there remains room for improvement for the suppression of bulk nonradiative recombination. General routes for suppressing recombination processes within the bulk and at interfaces are discussed. Finally, current challenges are presented, which need to be overcome in order to obtain a deeper insight into the nature of defects at surfaces and within the bulk of perovskites, and ultimately enhance the power conversion efficiency of perovskite solar cells toward their thermodynamic efficiency limit. [ABSTRACT FROM AUTHOR]

The deep‐level defects at grain boundary (GB) result in serious trap‐assisted non‐radiative recombination. Moreover, the degradation of perovskite films is preferentially triggered by the attack of GBs by water and/or oxygen. Therefore, it is urgently needed to develop a multifunctional GB tailoring strategy to address the abovementioned issues. Herein, a self‐formed multifunctional GB passivation strategy is reported, where an ultrathin GB passivation layer is in situ constructed via incorporating K2SO4 into perovskite precursor solution. The self‐formed GB passivation layer plays multiple functions, including crystallization improvement, defect passivation, and moisture resistance. The GB manipulation strategy endows perovskite films reduced defect density, boosted carrier lifetime, and thus suppressed non‐radiative recombination, which contributes to efficiency enhancement from 20.39% to 22.40%. The GB tailoring approach makes the unencapsulated target device exhibit no degradation while the control device degrades to 93% of its initial power conversion efficiency after 1200 h ambient exposure with a relative humidity of 10–20%. The modified device maintains 98% of its original efficiency after aging at 60 °C for 1200 h, whereas only 89% for the control device. Herein, the importance of developing an in situ GB modification strategy in enhancing performance of perovskite photovoltaics is highlighted. [ABSTRACT FROM AUTHOR]

Tunable crystal growth offering highly aligned perovskite crystallites with suppressed deep‐level defects is vital for efficient charge transport, which in turn significantly influences the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Herein, a "precursor to perovskite‐like template to perovskite" (PPP) growth strategy is developed, using either MAAc or GuaCl precursor to induce a sacrificial thermal–unstable perovskite‐like template for (FAPbI3)x(MAPbI3)y perovskite growth. The self‐sacrificed intermediate template induces the formation of highly aligned perovskite crystals with greatly enhanced film crystallinity and suppresses deep‐level defect formation. Furthermore, it is proved that MAAc or GuaCl completely evaporates during the high‐temperature annealing process. The reduction in defect densities and nonradiative recombination enhances both carrier lifetime and charge dynamics, yielding impressive PCEs of 22.3% and 22.8% with a high open‐circuit voltage (VOC) of 1.16 V and an incredible fill factor (FF) of 81.5% and 79.4% for MAAc‐ and GuaCl‐based devices, respectively. These results suggest that the formation of the thermal–unstable perovskite‐like sacrificial template is a promising strategy to restrain the deep‐level defects in perovskite films toward the attainment of highly efficient and stable large‐scale PSCs as well as other perovskite‐based electronics. [ABSTRACT FROM AUTHOR]

Interface engineering is widely applied in the one‐step antisolvent deposition for elevating efficiency of the perovskite solar cells (PSCs). Herein, an alcohol‐soluble small molecule, namely 2‐mercaptoimidazole (MI), is inserted between the hole transport layer and perovskite layer to form a cross‐linking bridge, which is built through: i) Coulomb interaction between the negatively charged MI and positively charged poly (3,4‐ethylene dioxythiophene); ii) electrostatic interaction between imidazolium cation and iodide anion in perovskite. The cross‐linking bridge can accelerate the hole transmission and inhibit interfacial recombination. Hence, by the optimum design of MI concentration, hysteresis‐free devices with a high power conversion efficiency of 20.68% are obtained. The overall efficiency increase is due to significantly enhanced short‐circuit current density from 21.28 to 23.45 mA cm−2 and slightly raised open‐circuit voltage from 1.06 to 1.08 V, suggesting that the MI modified layer can effectively improve the performance of the devices. Moreover, unencapsulated devices with MI interfacial modification show better environmental stability compared to the reference devices. This facile interfacial approach is promising for future commercialization of inverted PSCs. [ABSTRACT FROM AUTHOR]

Organometal halide perovskite solar cell enjoys a rapid development in the last decade. However, the severe J-V hysteresis existed in perovskite solar cells leads to an over- or under-estimation of device efficiency. Herein, we introduce an ammonium salt as a new dopant of perovskite. As a result, the J-V hysteresis is almost eliminated, and a higher average efficiency is obtained. Besides, the degradation under constant illumination in ambient atmosphere observed in control devices is greatly improved. Thin film characterizations reveal that the addition of ammonium salt leads to smoother, more homogenous and better crystalline perovskite films, which exhibit more intense photoluminescence and a little longer fluorescent lifetime. Such improvements are owing to the dual-functional sulfoxide (S O) in the dopant that can assist in perovskite crystallization and passivate the surface defects, thus giving rise to the eliminated J-V hysteresis. Our results provide an easy way to eliminate the J-V hysteresis in perovskite solar cell. [ABSTRACT FROM AUTHOR]

Recently, the thermally stable and facilely fabricated inorganic CsPbIBr2 perovskite solar cells (PSCs) have attracted tremendous attention where the electron transport layer (ETL) is vital. However, the typical sintering temperature for the widely used electron transport material, that is, TiO2, is more than 400 °C, elevating the cost and hindering the application. Due to high electron mobility and low fabrication temperature, ZnO becomes a desirable alternative for TiO2, as the ETL in CsPbIBr2 PSCs, albeit with low open‐circuit voltage (Voc). Herein, this work introduces a trace of NH4Cl to the sol–gel‐derived ZnO precursor to decrease the work function of the ZnO film, tune the surface morphology of the perovskite film, and thus suppress the density of trap states in the CsPbIBr2 films. Consequently, full‐coverage and pure‐phase CsPbIBr2 films consisting of micron‐size and high‐crystallinity grains are obtained. More importantly, for the optimal NH4Cl‐modified ZnO, a shining improvement in Voc from 1.08 to 1.27 V boosts the champion CsPbIBr2 PSCs to obtain a power conversion efficiency of 10.16%, which is the highest value reported among pure‐CsPbIBr2 PSCs under a low fabrication temperature of 160 °C. In addition, the NH4Cl‐modified ZnO ETL reduces the severe hysteresis and increases the device stability significantly. [ABSTRACT FROM AUTHOR]

Charge extraction at the active layer‐electrode interfaces is critical in obtaining highly efficient planar perovskite solar cells (PSCs). It is commonly achieved by enhancing the charge carrier mobility of the charge transfer layer (CTL) that possesses a desirable energy level. Nevertheless, the in‐plane movement of charge carriers in the CTL possibly leads to severe charge recombination in the presence of defects at the interfaces. To verify this overlooked possibility, herein, an oxidized monolayer of poly(3,4‐ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) hole transfer layer (HTL) is constructed by water rinsing followed by H2O2 oxidation. The oxidized PEDOT:PSS monolayer ensures a high charge transfer ability from perovskite to electrode, but at the same time limits in‐plane charge transport. An inverted planar PSC fabricated on the oxidized PEDOT:PSS monolayer yields a power conversion efficiency (PCE) of 18.8%, higher than 17.0% of the control device based on a pristine PEDOT:PSS monolayer. The main contribution comes from the fill factor (FF), which is as high as 82%. Characterizations indicate that the conjugation length of PEDOT chains is decreased after H2O2 oxidation, which lowers the conductivity of PEDOT:PSS HTL in the in‐plane direction. This study suggests that the charge recombination at the electrode interfaces due to in‐plane charge transport in the CTLs is not to be neglected. [ABSTRACT FROM AUTHOR]

Interfacial modification is an effective method to improve the performance of perovskite solar cells (PSCs). However, defects in SnO 2 itself and interfacial defects with perovskite (PVK) lead to the limited performance of PSCs. In this study, 3, 5-dibromobenzoic acid (3,5-DBBA) material was added at the interface between electron transport layer (ETL)and perovskite absorption layer. It was found that Br in 3,5-DBBA can passivate the oxygen vacancies and uncoordinated Sn4+ defects in SnO 2 , and optimize the interface contact between ETL and perovskite film, inhibit the non-radiative recombination of charge carriers, and improve the carrier lifetime and extraction yield. Br is also able to interact with the perovskite lattice to passivate Pb2+ defects and regulate the crystal growth of the perovskite. The open circuit voltage of perovskite solar cells was increased from 1.12 V to 1.16 V, and the power conversion efficiency was increased from 19.19 % to 22.27 %. The bromine templates strategy can also effectively improve the stability of PSCs. It provides a new strategy for realizing high performance perovskite solar cells. [ABSTRACT FROM AUTHOR]

Interface defect is one of the main factors that lead to non-radiative recombination of carriers at the interface and the decomposition of perovskites. This ultimately results in low efficiency and poor stability of perovskite solar cells (PSCs). Here, a passivated molecule called 2-Aminopyridine (2-APy) was proposed to reduce the defects of the interface between the perovskite and the hole transport layer. The results showed that the amino group in 2-aminopyridine can interact with the vacancy and free iodide ions on the surface of perovskite, thus passivating the defects at the interface and enhancing the hole transport capacity. As a result, 2-APy-modified PSCs exhibited inhibited non-radiative recombination, and the efficiency of PSCs increased to 21.46 %. The increase in the efficiency of PSCs is primarily seen in the rise of the open circuit voltage (V OC , from 1.12 to 1.15 V) and short circuit current (J SC , from 22.86 to 23.77 mA/cm2). This work demonstrates that pyridine is an effective group for passivating the defects between the perovskite layer and the hole transport layer. [ABSTRACT FROM AUTHOR]

Solvent engineering is a key aspect in the fabrication of high-quality perovskite films towards highly efficient perovskite solar cells (PSCs). However, the major solvents used in preparing the different solutions of PSC components are considered hazardous, which poses a significant threat to human beings or the environment. Besides, perovskite materials are reputed to exhibit serious environmental stability issues, limiting their production in ambient environment, thus hindering their practical applications. Therefore, it is of critical importance to develop eco-friendly strategies for fabricating PSC devices in ambient air, which will pave the way for industrial applications. In this review, the toxicity of commonly employed solvents was explored, and their greener alternatives were thoroughly examined. Advances in the development of green solvents for perovskite precursor solutions, as well as for the charge transport layers and their application in ambient environment were also discussed. Finally, an overall perspective is presented and key challenges limiting the development of eco-friendly PSC fabrication routes highlighted. [Display omitted] • Routinely used processing solvents are extremely toxic to humans and environment. • Latest significant studies using green solvents for PSCs in ambient air are studied. • Mechanism underlying the improved stability in ambient conditions is revealed. • Ionic liquids are the best for highly efficient and stable PSCs in ambient air. [ABSTRACT FROM AUTHOR]

We systematically review the progress of CsPb(I x Br 1− x) 3 solar cells in four aspects: phase stability, crystallization control, low-temperature preparation, and defect passivation. We propose challenges and future directions for developing highly efficient and stable devices. Owing to its nice performance, low cost, and simple solution-processing, organic-inorganic hybrid perovskite solar cell (PSC) becomes a promising candidate for next-generation high-efficiency solar cells. The power conversion efficiency (PCE) has boosted from 3.8% to 25.2% over the past ten years. Despite the rapid progress in PCE, the device stability is a key issue that impedes the commercialization of PSCs. Recently, all-inorganic cesium lead halide perovskites have attracted much attention due to their better stability compared with their organic-inorganic counterpart. In this progress report, we summarize the properties of CsPb(I x Br 1− x) 3 and their applications in solar cells. The current challenges and corresponding solutions are discussed. Finally, we share our perspectives on CsPb(I x Br 1− x) 3 solar cells and outline possible directions to further improve the device performance. [ABSTRACT FROM AUTHOR]

Realization of fast hole extraction is an effective route for the performance enhancement of inverted perovskite solar cells (PSCs). The precise bandgap tuning in perovskite layer has been expected to accelerate hole extraction. Therefore, in this report, we demonstrate a modified one-step fabrication method for the bandgap tuning of perovskite layer by designing iodide concentration gradient. Prior to the perovskite precursor solution spin-coated, different concentration of methanaminium iodide (MAI) solution was pre-coated on PEDOT:PSS layer to form iodide concentration gradient in perovskite layer. Fast hole extraction and short lifetime due to iodide concentration gradient was confirmed by photoluminescence measurement. By optimizing the MAI concentration with 4 mg/ml, the modified PSCs exhibited a power conversion efficiency of 16.67% due to an increase in short-circuit current density (J sc ) from 19.66 mA/cm 2 to 23.52 mA/cm 2 and an increase in open circuit voltage from 0.97 V to 1.01 V. These values are significantly higher than PSCs using conventional one-step fabrication method without pre-coated MAI layer, which exhibit efficiency of only 14.8%. We think that this new approach is an effective way to enhance the performance of PSCs. [ABSTRACT FROM AUTHOR]

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) has been widely used as the hole transport material in optoelectronic devices. To avoid the cross talk among different crossbars, PEDOT:PSS with low conductivity is required. It thus has a high loading of the non-conductive PSSH. The PSSH-to-PEDOT weight ratio is 6 for Clevios P VP Al 4083 that is the most popular polymer as the hole transport layer. However, the acidic PSSH brings severe problems to the device stability and performance. Here, PEDOT:PSS solutions with low acidity can be prepared through a facile treatment of PEDOT:PSS solution by probe ultrasonication. Two grades of PEDOT:PSS, Clevios PH1000 and Clevios P, with a PSSH-to-PEDOT weight ratio of 2.5 were treated by probe ultrasonication. The ultrasonication can lower the viscosity and the colloidal sizes of PEDOT:PSS solutions and conductivity of PEDOT:PSS films. The pH value of probe-ultrasonicated Clevios P was 2.12, higher than that (1.77) of pristine Clevios P VP Al 4083. The ultrasonication-treated PEDOT:PSS solutions were used as hole transport layer in polymer solar cells and perovskite solar cells. The photovoltaic performances of these solar cells are comparable to that of control devices employing Clevios P VP Al 4083 PEDOT:PSS as the hole transport layer. [ABSTRACT FROM AUTHOR]