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The poor film stability of Sn-Pb mixed perovskite film and the mismatched interface energy levels pose significant challenges in enhancing the efficiency of tin–lead (Sn-Pb) mixed perovskite solar cells. In this study, polyvinylpyrrolidone (PVP) is introduced into the PVK perovskite precursor solution, effectively enhancing the overall stability of the film. This improvement is achieved through the formation of robust coordination bonds between the carbonyl (C=O) in the pyrrole ring and the undercoordinated SnII and PbII, thereby facilitating the passivation of defects. Furthermore, the introduction of PVP inhibits the oxidation of tin (Sn), thereby enhancing the n-type characteristics of the perovskite film. This adjustment in the energy level of the PVK perovskite film proves instrumental in reducing interface energy loss, subsequently improving interface charge transfer and mitigating device recombination. Consequently, perovskite solar cells incorporating PVP achieve an outstanding champion power conversion efficiency (PCE) of 21.31%. [ABSTRACT FROM AUTHOR]

The bandgap of inorganic halide perovskites plays a crucial role in the efficiency of solar cells. Although density functional theory can be used to calculate the bandgap of materials, the method is time-consuming and requires deep knowledge of theoretical calculations, theoretical calculations are frequently constrained by complex electronic correlations and lattice dynamics, resulting in discrepancies between calculated and experimental results. To address this issue, this study employs machine learning to predict the bandgap of inorganic halide perovskites. The XGBoost classifier classifies ABX3-type inorganic halide perovskites into narrow and wide bandgap materials. The study collected a dataset consisting of 447 perovskites and generated material descriptors using the Matminer Python package. The model predicts narrow-bandgap materials with 95% accuracy. Finally, the Shapley analysis revealed that the key factor affecting the bandgap of perovskites is the electronegativity range. As the range of electronegativity increases, so does the possibility of a perovskite with a narrow bandgap. These findings highlight the powerful ability of machine learning to quickly and accurately predict the bandgap of perovskites. [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 the recently researched Sn-contained perovskite solar cells (PSCs), limited work is focused on corrosion of a metal electrode, which is recognized as the obstacle of efficient and stable devices. Here, it is found that a pure Sn based PSC shows the most serious and quick corrosion of an Ag electrode, compared with Pb and Sn–Pb PSCs. I2, SnOX, and AgI are the main products of the aged Ag electrode in Sn based PSCs, which greatly differed from Pb and Sn–Pb PSCs. Oxidation of FASnI3 under O2/H2O produces aggressive I2, together with gaseous FA and diffusive I−, degrading the PVK film and Ag electrode greatly. This work highlights the corrosion velocity and mechanism of Ag electrodes in Sn-contained PSCs, which may help to find out possible solutions to circumvent the instable issue. [ABSTRACT FROM AUTHOR]

The all-inorganic CsPbI3 perovskite presents promising prospects due to its suitable band gap and nonvolatile nature, while serious nonradiative recombination and unmatched energy level alignment hinder its further developments. Here, a facile and effective surface treatment strategy is proposed to modify the CsPbI3 surface with ethanolamine, leading to significantly reduced defects, and ameliorated band alignment and morphology. Consequently, a champion power conversion efficiency of 18.41% with improved stability is achieved for the inverted CsPbI3 solar cells. [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]

Efficient electron transport layer-free perovskite solar cells (ETL-free PSCs) are promising designs because they offer low-cost, simpler device configuration and greatly promote the large area flexible application of PSCs. Meanwhile, compared to traditional PSCs with ETL, the development of ETL-free PSCs is hindered by their low performance due to serious interfacial energy loss. Herein, we reveal that ETL-free devices with relatively low carrier lifetimes of perovskite films exhibit more substantial photogenerated carrier loss, resulting in a lower electron-injection rate at the FTO (fluorine-containing tin oxide)/perovskite interface, which is mainly responsible for the performance loss. Moreover, we demonstrate that improving the carrier lifetimes of perovskite films can remedy the poor carrier extraction efficiency at the FTO/perovskite interface through three typical perovskite films. Similarly, for all-inorganic perovskite with lower carrier lifetime and hole transport layer-free devices, prolonging carrier lifetime may be an important measure to improve the device performance. Benefiting from this discovery, increasing the carrier lifetime of the perovskite films can counterbalance the inferior device interfaces, endowing the ETL-free PSCs with high performance close to that of the ETL devices. Our research provides insights into ETL-free PSCs and offers opportunities for high-performance ETL-free PSC device design. [ABSTRACT FROM AUTHOR]

CsPbI2Br all-inorganic perovskite solar cells (PSCs) have attracted much attention due to their suitable bandgap and outstanding thermostability. However, the large energy loss of CsPbI2Br PSCs generally endows low open circuit voltage (VOC) and unsatisfactory power conversion efficiency (PCE), which severely hamper its further development. Herein, we proposed a facile route to modify the ZnO electron transporting layer (ETL) by in situ chemical doping strategy with metal ions. The doped ZnO ETL with Pb(Ac)2 or CsAc cannot only effectively tune its energy levels, conductivity, and charge extraction but also ameliorate the crystallization and morphology of upper perovskite films. Particularly, Pb(Ac)2-doped ZnO (ZnO:Pb) induces an energy level offset of 0.15 eV relative to the conduction band of CsPbI2Br with largely reduced Ohmic loss. Thus, the highest VOC is significantly boosted to above 1.3 V for the CsPbI2Br PSCs with a champion PCE of 16.36%, while the reference PSC just yields a moderate PCE of 14.43% with a low VOC of 1.168 V. Moreover, considerable improvements in device stability are achieved for the PSCs with doped ZnO ETLs than those of the ZnO-based device. Our work provides a promising strategy to alleviate the VOC deficit toward the attainment of highly efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

In inverted perovskite solar cells, the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/Ag back interface is quite important because serious recombination occurs and H2O/O2 directly attacks this interface to induce device instability. Here, bi-functional dipole layers are applied at the interface aiming at improving the charge transport and device stability simultaneously. Silane with -CF3 end group anchored on the PCBM surface induces more effective dipole effect than that with (CH2)7-CH3 end functional silane, bending the interface energy level to promote electron transport and reduce recombination. The hydrophobic nature of -CF3 also enhances the durability of the device. This work highlights the back surface dipole management method to achieve efficient and stable perovskite solar cells. [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]

All-inorganic halide perovskites (AIHPs) have become one of the most promising materials for commercial perovskite photovoltaics owing to their enhanced efficiency and thermodynamic stability. Output instability, such as current hysteresis, is stressed in organic-inorganic hybrid perovskite photovoltaics but is neglected in AIHP solar cells. Here, the origin and suppression of current hysteresis in AIHP solar cells are addressed from a microscopic viewpoint. The incorporation of fullerene into AIHP films efficiently suppresses ion migration, which alleviates the macroscopic current hysteresis in solar cells. This result is confirmed by both Kelvin probe force microscopy and conductive atomic force microscopy measurements. Our results provide an advanced understanding of the microscopic properties of AIHPs but also clearly clarify how to suppress the macroscopic current hysteresis, which further inspires the optimization of solar cells up to the levels of organic–inorganic hybrid counterparts. [ABSTRACT FROM AUTHOR]

The tunability of the carrier/conduction polarity of halide perovskite via intrinsic defect self-doping makes it possible to implement a simple p–n heterojunction perovskite solar cell. Here, approaching 16% efficient prototype device of the p-type spiro-MeOTAD/n-type MAPbI3 heterojunction perovskite solar cell is demonstrated via synergetic energy band and interface engineering. The n-type perovskite is enabled by self-doping associated with excess PbI2, avoiding a redundant electron transport layer, while the oxygen-induced p-type extrinsic doping (oxidation) of spiro-MeOTAD ensures its high hole conductivity and Ohmic contact with Au back electrode. Furthermore, ITO's effective work function is reduced by the polar molecular modification layer to ensure its Ohmic contact with perovskite. Also, the functional groups of this modification layer effectively passivate the front interface defects, contributing to the enhanced device performance observed. This work highlights the great potential of facile energy band and interface engineering for efficient and simple-structured perovskite solar cells. [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]

To realize high-performance perovskite solar cells (PSCs) ensuring low-cost flexible application with low energy consumption, efficient electron transport layers (ETL) that can be processed at low temperatures are desired. In this contribution, low temperature (about 70 °C) UV/ozone irradiation was applied to synthesis crystallized TiO 2 films as ETL. The UV exposure induces photo-catalytic removal of the organic ligands and spontaneous coalescence of the TiO 2 framework, resulting in excellent TiO 2 films with considerable crystallinity. UV irradiation induces both complete removal of organic media and more efficient charge collection. Accordingly, planar heterojunction (PH) PSCs with such ETL exhibited outstanding photovoltaic performance up to 17.03%, which is even higher than the value (12.98%) of counterpart device with high temperature thermal sintered TiO 2 ETL (without TiCl 4 treatment). These low temperature solution-processed TiO 2 films by facile UV irradiation are suitable for the low-cost, large yield solution process on a flexible substrate for photoelectric devices. [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]

Rough dense sol-gel-derived titanium dioxide (TiO 2 ) electron-transport layers (ETLs) and smooth organolead halide perovskite (PVK) films for pseudo-planar heterojunction perovskite solar cells (P-PH PVKSCs) were fabricated by a facile one-step dip-coating method. The highly compact TiO 2 ETLs and uniform PVK films endow the device a high power conversion efficiency (PCE) of over 11%, which was nearly identical to that of a reference device (12%) fabricated by conventional spin-coating. Furthermore, the device showed no pronounced hysteresis when tested by scanning the voltage in a forward and backward direction, showing the potential of facile and waste-free dip-coating in replacing of spin-coating for large area perovskite solar cells preparation. Lastly, the hysteresis was compared and discussed and models regarding the abnormal hysteresis, roll-over and current peak phenomena were proposed as well. [ABSTRACT FROM AUTHOR]

Device modeling of CH 3 NH 3 PbI 3−x Cl x based electron transport layer-free planar perovskite solar cells was performed. The simulation was conducted by the program SCAPS (Solar Cell Capacitance Simulator). With appropriate physical parameters, a high open-circuit voltage of 1.04 V close to results reported experimentally was successfully reproduced in the simulation. Simulation results revealed a great dependence of PCE on the thickness and defect density of the perovskite layer. An optimum perovskite thickness of about 500 nm was confirmed and it well consistent with the thickness range of real devices was derived. Meanwhile, parameters including the FTO/perovskite interface defect density as well as the doping concentration of the front contact (FTO) were identified to significantly influence the performance of the device. In particular, the interface quality at the FTO/perovskite interface has greater impact on the device parameters than that at the perovskite/HTL interface, which suggests that more attention should be paid to the front FTO/perovskite interface to further enhance the performance of electron transport layer-free device. Appropriate interface defect passivation to reduce the interface defect density to the order of ~10 15 cm −3 is necessary and urgently needed. Lastly, the effect of the electron and hole mobility and carrier diffusion length of CH 3 NH 3 PbI 3−x Cl x were also analyzed and the results revealed that the mobility and diffusion length experimentally reported (~1.0 µm) are large and long enough for high efficiency. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PVKSCs) are an attractive technology that finds their potential in the field of renewable energy sources. Transparent conductive oxides including fluorine-doped tin dioxide (FTO) and indium tin oxide (ITO) with high optical transmittance and low electrical resistivity are key components in PVKSCs. While commercial FTO or ITO either requires high temperature and high vacuum process or contains rare indium element, which will increase the production cost of PVKSCs. Here we report efficient electron-transport layer (ETL) free planar PVKSCs using the recycled FTO/glass substrates from degraded devices. By simple and low-temperature processes including organic solvent washing, ultrasonic cleaning and UV ozone treatment, the discarded substrates can be readily reused for fabricating ETL-free planar PVKSCs. The UV–vis optical transmission, crystal structure, sheet resistance, surface morphology, elemental composition and static contact angles measurement of the original and recycled FTO/glass substrates (one time and two times) were measured and compared. Planar ETL-free devices with power conversion efficiencies of about 10% have been achieved by adopting the recycled FTO/glass substrates, which are comparable to that of the devices based on the original FTO substrates, suggesting the feasibility of recycling the FTO/glass substrates from degraded devices for fabricating ETL-free PVKSCs. [ABSTRACT FROM AUTHOR]

Planar perovskite solar cells with a p–i–n structure use both hole-transport layers and electron-transport layers to promote collection of photogenerated holes and electrons for achieving high performance, wherein a high temperature processed compact and mesoporous titanium dioxide are usually required. We report here efficient perovskite solar cells grown directly on ultraviolet–ozone treated fluorine-doped tin oxide (FTO) substrates without using any electron-transport layers. The morphology, structure, optical–electrical properties of perovskite films deposited on FTO substrates with and without ultraviolet–ozone treatment and their corresponding devices׳ performance have been studied and compared. Ultraviolet–ozone treatment of FTO substrates improves the smoothness and coverage of CH 3 NH 3 PbI 3− x Cl x films, which avoids direct contact between FTO and hole-transport layer. A planar electron-transport layer free device with a power conversion efficiency of over 10% has been achieved, suggesting that the widely adopted electron-transport layer is not a requirement for an efficient device. [ABSTRACT FROM AUTHOR]

We report planar heterojunction perovskite solar cells with tetrafluoro-tetracyanoquinodimet-hane (F4-TCNQ) doped spiro-MeOTAD by solvent treatment as hole transport layer. The non-hygroscopic F4-TCNQ doped spiro-MeOTAD plays the same role as Li-bis (trifluoromethanesulfonyl) imide doped spiro-MeOTAD in perovskite solar cells, endowing the device both high efficiency and good stability. The F4-TCNQ dopant was optimized to enhance the conductivity and adjust the highest occupied molecular orbital of spiro-OMeTAD to match the valence band maximum of perovskite for efficient hole extraction, which results in a high fill factor, open circuit voltage and short current density, simultaneously. Device including the F4-TCNQ doped spiro-MeOTAD exhibits a power conversion efficiency of 10.59%, which is a 160% improvement relative to that of the control device with the pristine spiro-MeOTAD as hole transport layer. Time-dependent solar cell performance measurements revealed significantly improved air stability for perovskite solar cells with the F4-TCNQ doped spiro-MeOTAD hole transport layer. [ABSTRACT FROM AUTHOR]

The morphology, structure, optical and electrical properties of perovskite films treated by two different annealing methods with different annealing temperature ramp and their corresponding device performance have been studied and compared. Annealing temperature ramp significantly influences the surface morphology and optical properties of perovskite films which determines the performance of solar cells which determines the performance of solar cells . The perovskite films treated by one-step direct annealing method tend to exhibit irregular and weak ultraviolet–visible absorption spectrum, which can easily result in great variation in the final performance of solar cells. While multi-step slow annealing is beneficial for preparing highly uniform and well-crystallized perovskite films, and thus these devices present tightly-distributed performance parameters. The best device treated by multi-step slow annealing method showed a short circuit current density of 21.49 mA/cm 2 , an open circuit voltage of 0.988 V, a fill factor of 64.86%, and a power conversion efficiency (PCE) of 13.58%, which is a 57% enhancement of the overall PCE relative to 8.65% of the device treated by one-step annealing method. These findings suggest that optimized slow temperature ramp is necessary to prepare high-efficient and well-reproducible perovskite solar cells. [ABSTRACT FROM AUTHOR]

Perovskite solar cells as a hot research topic show the necessity of controlling the interface. In this work, an insulating alkyl chain layer is self-assembled at the perovskite/hole transport material interface, which successfully exhibits a dual function: blocking electron recombination and resisting moisture at the same time. Improved solar energy conversion efficiency and stability of the device are both achieved. [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]

CH3NH3PbI3 perovskite films with full coverage and negligible roughness have been obtained by the two-step sequential thermal evaporation (TSSTE) process, which are further applied to fabricate thin-film transistors (TFTs). To gain the optimal electrical characteristics in our TFTs, the effect of the evaporation amount of PbI2 on the crystallization and thickness of CH3NH3PbI3 films is studied during the process of TSSTE. As a result, we demonstrate a thin-film field-effect transistors possessing a hole field-effect mobility of 3.55 cm2 V− 1 s− 1 as well as on/off ratio greater than 105 with the optimal CH3NH3PbI3 films as the channel layer. Through a further comparative analysis, MoO3 buffer layer is inserted between the perovskite channel layer and the source-drain electrode to improve the contact resistance of TFTs. As an understanding of device mechanism, a fact that insertion of MoO3 buffer layer into the Au/perovskite interface significantly reduced the contact resistance from 705 to 0.2 kΩ cm is unveiled. By inserting MoO3 buffer layer, the hole field-effect mobility of the CH3NH3PbI3 organic-inorganic hybrid TFTs can reach to 7.47 cm2 V− 1 s− 1. [ABSTRACT FROM AUTHOR]

Long-chain insulating polymers dissolved in perovskite precursor solution can assemble the polymer scaffold acted as the function of TiO 2 porous layer to improve the quality of the perovskite films. Here, perovskite films with high electronic quality were prepared by mediating nucleation and crystal growth. Polymer post treatment can induce Lewis acid-base reaction with PbCl 2 , which alleviates the reaction velocity between PbCl 2 and CH 3 NH 3 I, and then retard perovskite crystallization. The interactions between the perovskite films and polymer with different concentration are addressed to interpret the function and evolution of the polymer long-chains during the annealing process. These solar cells exhibit efficiency more than 15% with small variation. Our work demonstrates the value of retarding nucleation and crystal growth by Lewis acid-base adducts for high-quality perovskite films. [ABSTRACT FROM AUTHOR]

• The oxidative I 2 /I 3 − in Sn-Pb perovskite is effectively eliminated to stabilize Sn2+. • The movable I− is successfully neutralized, protecting the Ag counter electrode from corrosion. • The solar cell device shows promoted photovoltage and efficiency with enhanced stability. In recent hotly researched tin–lead (Sn-Pb) mix perovskite solar cells (PSCs), the oxidation of Sn2+ is not an isolated process but accompanied by the oxidation of I− to I 2 , which are both responsible for the severe p-doping and complex defect situation. Diffusion of interstitial I further severely corrodes the metal electrode to fail the PSC. Thereby, managing the I− oxidation and meanwhile neutralizing the movable I− together with suppressing Sn2+ oxidation is quite a challenge for efficient and stable Sn-Pb PSCs. In this work, a natural reductive amino acid (DOPA) is introduced into perovskite layer to successfully inhibit the oxidation of both Sn2+ and I−, at the same time, neutralize the diffusive I− to protect the Ag electrode from corrosion. Benefiting from the improved chemistry situation, the DOPA doped PSC shows significantly promoted photovoltage and efficiency at AM1.5, with enhanced light and shelf stability. This work highlights the importance of I defects management to achieve efficient and stable Sn-Pb PSCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • A facile surface modification method using alkylamines to treat the CsPbI 3 surface is proposed. • HDA treatment can ameliorate defect passivation and energy level alignment to reduce voltage loss. • A champion PCE of 18.21% is achieved for the HDA-treated inverted CsPbI 3 PSCs. • HDA treatment promotes the humidity stability both of CsPbI 3 films and solar cells. Inorganic CsPbI 3 perovskite has been regarded as a kind of promising light-harvesting material due to its outstanding photoelectrical characteristics especially in perovskite solar cells (PSCs). However, there are still some problems hindering its further development, among which non-radiative recombination induced by traps and voltage loss are very pivotal. Here, the passivation of surface defects and energy level alignment of perovskite films are greatly ameliorated by facile surface modification with alkylamines. It is found that the undercoordinated Pb2+ are effectively passivated by the terminal amino group, leading to significantly reduced surface trap density, while the charge lifetime of treated perovskite films is prolonged. Besides, the bilateral amino groups from hexanediamine (HDA) can provide additional hydrogen bond to coherently connect the PbI 6 4− octahedra. Moreover, gradient energy levels are created after surface treatment, which promote the carriers transfer and reduce the voltage deficit. Consequently, a champion power conversion efficiency (PCE) of inverted CsPbI 3 PSCs over 18 % with higher fill factor (FF) of 81.21 % and open circuit voltage (V OC) of 1.10 V is obtained compared to the pristine device with a lower PCE of 12.69 % (V OC of 1.01 V, and FF of 62.49 %). Besides, the unencapsulated device with HDA treatment exhibits good stability with keeping 80 % of its initial efficiency after being aged for 1000 h at 35 % relative humidity. Our work can offer a facile but effective approach for the development of highly efficient and stable inverted CsPbI 3 PSCs. [ABSTRACT FROM AUTHOR]

Inorganic nickel oxide (NiO x)-based inverted perovskite solar cells (PSCs) are reported to be more stable compared to those using organic hole transport layer materials. However, the Fermi level of NiO x is relatively away from the valence band of perovskite (PVK) layer, causing a large energy level shift at the NiO x /PVK interface and a weak built-in electric field strength. These increase the possibility of recombination, reduce the effective charge collection, seriously affect the efficiency of the device. In this work, an interface dipole with -CF 3 end group is anchored to the NiO x /PVK interface, leading to a more matched energy level structure and greatly reducing the energy barrier at the NiO x /PVK interface. Moreover, the addition of Si-CF 3 significantly improves the conductivity of NiO x and blunts the defects to large extent. The dipole interlayer significantly improves the built-in electric field and thus increases the photovoltage. Ultimately, the modified device achieves a score of 19.58% efficiency, much better than 17.98% of the control device. [Display omitted] [ABSTRACT FROM AUTHOR]

A rapid annealing technique for fabricating perovskite materials via microwave radiation in air condition is presented. A planar-heterojunction perovskite device via microwave radiation within 6 min exhibits an efficiency of 10.29%, compared to 11.08% for a 90 min heating-annealed device in inert atmosphere, which is higher than that (8.04%) of a heating-annealed device in air condition under high humidity (∼60%). We believe that the microwave annealing technique provides a fast and less energy-intensive process for fabricating ideal perovskite active layers for high performance solar cells. [ABSTRACT FROM AUTHOR]

• Formation of (TMA) x FA 1-x Pb(PF 6) x I 3-x /FAPbI 3 heterojunction through interface ion exchange. • Strong hydrogen bonding and ion size effect stabilize the phase structure. • A champion efficiency of 21.43% was obtained with greatly enhanced device stability. Though formamidinium lead triiodide FAPbI 3 is hotly researched, it still suffers from chemical and phase instabilities, arising from inherent weak chemical bonding and easily transformed crystal configures respectively. This induces depraved opto-electronic properties and device instability, which is imperative to be solved. Here, chemical interaction enhancement in heterostructure of (TMA) x FA 1-x Pb(PF 6) x I 3-x /FAPbI 3 simultaneously improves the chemical and phase stability with preserving its inherent bandgap. Strong hydrogen bonding between PF 6 - and FA+ drastically reduces the α phase formation energy and diminishes the interface trap states. The resulting perovskite solar cells achieve improved efficiency of 21.43% compared with 19.32% of the control device. Meanwhile, ∼90% and 80% of the initial efficiency are maintained for unpacked devices after 1200 h storage (25 °C, 30% relative humidity) and 300 h maximum power point tracking (1 sun, 25 °C, N 2), outperforming the control one. This work highlights a robust interface construction method to overcome the inherent problem of FAPbI 3. [ABSTRACT FROM AUTHOR]

• The fluorine atom has induced electrostatic potential and dipole moment change. • Cl- doping can enhance crystallization and prevent phase change. • The champion device achieves a PCE of 16.29% and the humidity stability is improved. [Display omitted] All-inorganic CsPbI 2 Br material has attracted considerable attention due to its good balance between phase stability and absorption capacity. However, the power conversion efficiency (PCE) and device stability of CsPbI 2 Br-based perovskite solar cells (PSCs) still lag far behind those of their counterparts, mainly deriving from the notoriously poor moisture stability under humid environment and large serious charge recombination. Herein, a typical phenethylammonium chlorine (PEACl) and its fluorinated derivative 4-fluoro-phenethylammonium chlorine (F-PEACl) are individually incorporated to modify the surface of CsPbI 2 Br film to ameliorate the above issues. Benefiting from the comprehensive passivation effect of ammonium halogen, the trap states of treated CsPbI 2 Br are vastly suppressed. In particular, fluorination significantly increased the dipole moment and hydrophobic property of F-PEACl. Thus, the present CsPbI 2 Br PSC achieves a champion PCE of 16.29% with high open-circuit voltage of 1.272 V, while the reference device and PEACl-treated device yield PCEs of 14.30% and 15.64%, respectively. More importantly, the PSC with F-PEACl capping layer retains 87.2% of its initial PCE after 1000 h storage under 20% RH ambient without encapsulation. Our results reveal the underlying mechanism of performance improvement by surface passivation strategy and provide an effective approach to further boost the CsPbI 2 Br PSC efficiency and stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • HEMA additive was added to the CsPbI 2 Br precursor solution to improve crystallization. • HEMA molecules could passivate defects and suppress charge recombination. • A champion efficiency of 16.13% was obtained with greatly enhanced device stability. CsPbI 2 Br all-inorganic perovskite has attracted considerable attention due to its high thermal stability and suitable bandgap, while the unsatisfactory crystallization quality and moisture instability significantly hinder its further application. Herein, a novel multifunctional liquid additive, 2-hydroxyethyl methacrylate (HEMA), is introduced into the CsPbI 2 Br precursor to ameliorate the above issues. Our results demonstrate that the functional groups of HEMA can interact with perovskite precursor, thus improving crystallization and passivating defects at the same time, and leading to a champion power conversion efficiency of up to 16.13%. Importantly, HEMA molecule in perovskite films will polymerize to a hydrophobic polymer at grain boundaries through breaking C = C bonds during the high temperature annealing process (160 °C). Moreover, this multifunctional liquid additive strategy endows perovskite films with promoted moisture tolerance by crosslinking perovskite grains and blocking moisture penetration, thus the unencapsulated device maintains 78% of its initial efficiency after aging at 30% relative humidity for 1000 h. These results demonstrate that the additive engineering with multifunctional molecule is applicable strategy for developing CsPbI 2 Br all-inorganic perovskite solar cells with both high efficiency and stability. [ABSTRACT FROM AUTHOR]