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Tin‐lead (Sn‐Pb) mixed perovskite with a narrow bandgap is an ideal candidate for single‐junction solar cells approaching the Shockley‐Queisser limit. However, due to the easy oxidation of Sn2+, the efficiency and stability of Sn‐Pb mixed perovskite solar cells (PSCs) still lag far behind that of Pb‐based solar cells. Herein, highly efficient and stable FA0.5MA0.5Pb0.5Sn0.5I0.47Br0.03 compositional PSCs are achieved by introducing an appropriate amount of multifunctional Tin (II) oxalate (SnC2O4). SnC2O4 with compensative Sn2+ and reductive oxalate group C2O42− effectively passivates the cation and anion defects simultaneously, thereby leading to more n‐type perovskite films. Benefitting from the energy level alignment and the suppression of bulk nonradiative recombination, the Sn‐Pb mixed perovskite solar cell treated with SnC2O4 achieves a power conversion efficiency of 21.43%. More importantly, chemically reductive C2O42− effectively suppresses the notorious oxidation of Sn2+, leading to significant enhancement in stability. Particularly, it dramatically improves light stability. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have shown an impressive power conversion efficiency of 26.1%, while their upcoming commercialization urgently needs to solve the stability problem. Among numerous stability issues of PSCs, little attention is paid to reverse bias stability. When some cells of the module are shaded by irresistible factors, this will cause the current of the illuminated part to flow through the shaded cells as a reverse current and force them to be under reverse bias. Herein, the breakdown mechanism dominated by different reverse bias regions of a prototype electron transport layer free PSCs is distinguished. And, it is confirmed that PSCs present a thought‐provoking dynamic reverse bias (DRB) behavior and variable reverse breakdown voltage (VRB), which is essentially distinct from classic solar cells. Specifically, VRB is significantly affected by voltage scan rate, range and direction, and illumination. The underlying mechanism is explained by drift‐diffusion modeling taking into account the electric field generated by directional ion migration. The latter can hinder the movement of charge carriers and cause the observed variable VRB and DRB behavior. Predictably, the understanding of the dynamic process is crucial to establish a standard VRB measurement procedure and further promote the commercialization of PSCs. [ABSTRACT FROM AUTHOR]

In recent years, the power conversion efficiencies of halide perovskite solar cells (PSCs) have reached 25.7%. Further commercialization puts forward higher requirements for the stability of PSCs under different stresses. Current research on the stability of PSCs predominantly focuses on investigating the effects of temperature, humidity, oxygen, ultraviolet light, and electrical bias stress, while stability under reverse bias has been poorly studied among the many factors. When large‐area application of PSCs panels occurs, the shading effect and local hot spots of PSCs modules in real scenarios all indicate that the research on reverse bias stability of PSCs is urgently needed. Within this review, a bird's‐eye view of the recent advances on the reverse bias stability issue and reverse bias behavior of PSCs is obtained, and the related mechanisms behind that have been proposed so far are reviewed and discussed. Furthermore, future directions are provided for further improving the reverse bias stability of PSCs via increasing the reverse breakdown voltage (VRB). This review aims to promote the establishment of well‐established reverse bias degradation and reverse breakdown mechanisms of PSCs as well as to establish standardized test procedures for reverse bias stability issues on the road to commercialization of PSCs. [ABSTRACT FROM AUTHOR]

Quasi‐two‐dimensional (quasi‐2D) organic–inorganic hybrid perovskites have shown excellent ambient stability with decent photovoltaic performance. Further improvement of device level properties requires a comprehensive understanding of the performance‐limiting mechanisms such as phase segregation, ion/electron coupling conduction, and their effects on charge transport at both the micro‐ and macro‐scale. Here, space resolved investigations of Ruddlesden–Popper (RP) phases of the commonquasi‐2D perovskite are probed using two complementary methods, conducting atomic force microscopy (c‐AFM) and Kelvin probe force microscopy (KPFM). Bias‐driven photocurrent mappings obtained by c‐AFM measurements disclose local inhomogeneous conduction and hysteresis currents in quasi‐2D RP perovskites, while relatively uniform conductivity is observed on individual grains. Bias‐driven KPFM reveals that the surface average photovoltage sign is dominated by the band bending at the buried perovskite–substrate interface. The quasi‐2D RP film exhibits substantial variations in the spatial response of the photovoltage across grains and grain boundaries, which is direct evidence of the inherently benign nature of microstructures, and the final device performance. This research elucidates underlying space‐resolved photoresponse mechanisms behind the lower efficiency of quasi‐2D RP perovskites compared with the 3D perovskites, which is necessary for further development of efficient and stable 2D perovskite‐based devices. [ABSTRACT FROM AUTHOR]

The pursuit of high power conversion efficiency (PCE) and cost‐effective perovskite solar cells (PSCs) has spawned many innovative device structure designs. Compared with the traditional NIP type PSCs, electron transport layer (ETL) free PSCs have attracted growing attention due to their enormous potential in large area, low‐cost flexible application. However, there is still a lack of in‐depth understanding of the energy level arrangement indium tin oxide (ITO)/perovskite interface, resulting in poor device performance. Here, a metal/insulator/n‐type perovskite/p‐type spiro‐MeOTAD (MINP) structure is proposed to elaborate on the influence of the apparent work function and contact barrier change of the metal–semiconductor (MS) and metal–insulator–semiconductor (MIS) junction on the carrier transfer and collection. Common and easily available 5‐amino‐valeric acid is inserted into the ITO/perovskite interface to form an insulating dipole layer and to ensure quasi‐ohmic contact at the front interface. Consequently, the device changes from Schottky/PN cascade heterojunction type to a single PN heterojunction device with its ideal factor decreasing from 3.35 to 2.05. Accordingly, the champion device achieves 19.37% PCE with significantly increased Voc and FF compared to the pristine device. This work provides a facile and effective method to improve the application potential of novel ETL‐free PSCs. [ABSTRACT FROM AUTHOR]

Electron transport layer (ETL)‐free perovskite solar cells (PSCs) have witnessed great progress via material and interface engineering. Enlighten by the wisdom from an old story of efficient silicon solar cells design, highly efficient MINP (metal/insulator/n‐type perovskite/p‐type spiro‐MeOTAD) PSC with polar insulating inter‐layer (PIIL) modified fluorine‐doped tin oxide (FTO) is reported as electron selective contact. The PIIL forms metal‐insulator‐semiconductor (MIS) junction with FTO and perovskite layer, while the n‐type perovskite forms P‐N junction with p‐type spiro‐MeOTAD. Unlike the classic MINP silicon solar cells where the I‐layer is usually neutral tunneling layer, the PIIL here optimizes the energy level alignment at the FTO/perovskite interface with its intrinsic electronic polarity while acting as an effective tunneling layer. Also, the functional group of the PIIL passivates the FTO/perovskite interface defects thus suppressing carrier recombination thereof and enhancing all device performance parameters simultaneously. Accordingly, the power conversion efficiency is greatly improved from 12.82% to 19.75%. With the enhanced electron collection and decreased carrier recombination of the MIS junction, this collaborative effect of interface engineering and defect passivation contribute to more stable ETL‐free PSC with less hysteresis. This work highlights the potential of novel device and interface design for simple‐structured, efficient and cost‐effective PSCs. [ABSTRACT FROM AUTHOR]

Efficient electron transport layer–free perovskite solar cells (ETL‐free PSCs) with cost‐effective and simplified design can greatly promote the large area flexible application of PSCs. However, the absence of ETL usually leads to the mismatched indium tin oxide (ITO)/perovskite interface energy levels, which limits charge transfer and collection, and results in severe energy loss and poor device performance. To address this, a polar nonconjugated small‐molecule modifier is introduced to lower the work function of ITO and optimize interface energy level alignment by virtue of an inherent dipole, as verified by photoemission spectroscopy and Kelvin probe force microscopy measurements. The resultant barrier‐free ITO/perovskite contact favors efficient charge transfer and suppresses nonradiative recombination, endowing the device with enhanced open circuit voltage, short circuit current density, and fill factor, simultaneously. Accordingly, power conversion efficiency increases greatly from 12.81% to a record breaking 20.55%, comparable to state‐of‐the‐art PSCs with a sophisticated ETL. Also, the stability is enhanced with decreased hysteresis effect due to interface defect passivation and inhibited interface charge accumulation. This work facilitates the further development of highly efficient, flexible, and recyclable ETL‐free PSCs with simplified design and low cost by interface electronic structure engineering through facile electrode modification. [ABSTRACT FROM AUTHOR]

The development of organometal halide perovskite solar cells has grown rapidly and the highest efficiency of the devices has recently surpassed 22%. Because these solar cells contain toxic lead, a sustainable strategy is required to prevent environmental pollution and avoid healthy hazard caused by possible lead outflow. Here, in situ recycling PbI2 from thermal decomposition CH3NH3PbI3 perovskite films for efficient perovskite solar cells was developed. The thermal behavior of CH3NH3PbI3 perovskite and its individual components were examined by thermogravimetric analysis. By optimizing the process of thermal decomposition CH3NH3PbI3 film, the complete conversion from CH3NH3PbI3 to pure PbI2 layer with a mesoporous scaffold was achieved. The mesoporous structure readily promotes the conversion efficiency of perovskite and consequently results in high-performance device. A perovskite crystal growth mechanism on the mesoporous PbI2 structure was proposed. These results suggest that in situ recycled PbI2 scaffolds can be a new route in manipulating the morphology of the perovskite active layer, providing new possibilities for high performance. Meanwhile, the risk of lead outflow can be released, and the saving-energy fabrication of efficient solar cells can be realized. [ABSTRACT FROM AUTHOR]

We investigated the impact of annealing atmosphere on the properties of organic-inorganic perovskite films systematically, and the mechanism is elucidated in perspective of crystallization kinetics of perovskite. It is found that the kind of gas, the state of the gas and the existence of solvent during annealing can affect the crystallization process of perovskite films, which therefore influence the morphology of perovskite films. In addition, the perovskite-based thin-film field-effect transistors were fabricated in different heating environment. It was discovered that the effect of annealing atmosphere on the performance of transistors is consistent with that on the crystallization qualities of perovskite films, which further confirms the influence of annealing atmosphere on the electronic properties of perovskite films. We also found that the type of gas has impact on the electronic properties of perovskite thin films probably by influencing the defects in the surface of perovskite films. Furthermore, it is notable that we confirmed that perovskite based transistors, of which the active layer was completely fabricated in air, show better performance, which is beneficial for commercial production of perovskite based transistors with low cost. [ABSTRACT FROM AUTHOR]

A facile and low‐temperature solution processed UV/ozone process has been proposed for fabricating TiO2 layer, making it possible to fabricate planar perovskite solar cells at low temperature. UV/ozone photo‐annealing treatment could easily eliminate the organic components, resulting in high quality amorphous TiO2 films with high transparency, electrical conductivity, and hydrophilicity. In addition, perovskite solar cells with the UV/ozone‐treated TiO2 electron transport layer exhibiting the best power conversion efficiency of 11.58% for rigid substrate and 7.33% for flexible substrate, respectively. The results clearly indicate that UV/ozone photo‐annealing treatment is a simple and effective process of fabricating high performance flexible perovskite solar cells. Fully low‐temperature solution‐processed perovskite solar cells (PSCs) are fabricated using UV/ozone (UV/O3) treated TiO2 film as an electron transport layer. UV/O3 treatment increases the electrical conductivity and wettability of the TiO2 film, and therefore improves the performance of PSCs. By optimizing the processing time of UV/O3 treatment, the power conversion efficiency of the best rigid and flexible device is 11.58% and 7.33%, respectively. [ABSTRACT FROM AUTHOR]

Electron transport layer (ETL)‐free perovskite solar cells (PSCs) are getting much more attention with their simpler structure and potentially low cost as well as higher stability. However, the elimination of ETL (such as TiO2) with intrinsically deep valance band level leads to the absence of the hole blocking mechanism and thus serious charge recombination at the FTO/perovskite interface compared with ETL‐based devices. An interface band bending associated built‐in electric field is an essential driving force of charge separation. Here, by intentional polarity tailoring of perovskite via incorporation of Sb as a shallow donor, ETL‐free PSCs with optimized energy level alignment both at the front and rear interfaces are constructed, resulting in an enhanced built‐in electric field and thus efficient majority carrier collection and minority blocking as well as reduced interfacial charge recombination at both interfaces. Device simulation calculations also confirm the importance of polarity control for device performance improvement. The effect of doping on the perovskite films properties and device performance are systematically demonstrated. Correspondingly, ETL‐free PSCs with a champion power conversion efficiency of 12.62% is achieved. N‐type Sb3+ heterovalent doping is conducted to regulate the polarity of perovskite and to optimize the interface band structure of ETL‐free PSCs. With doping, the band bending at both FTO/perovskite and perovskite/spiro‐MeOTAD interfaces ensures efficient collection of majority carrier and blocking of minority carrier, contributing to 12.62% efficient ETL‐free device with a Schottky/p‐n cascade heterojunction, pointing out new insights into the understanding of such devices. [ABSTRACT FROM AUTHOR]