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More and more attention has been paid to CsPbIBr2 material for perovskite solar cells (PSCs), owing to the trade-off between bandgap and stability. However, the reported maximum power conversion efficiency (PCE) of CsPbIBr2 PSCs is lag behind that of the congeners due to the serious interface recombination of charge carriers. In this work, the effects of interface defect density and interface band offset on the properties of CsPbIBr2 PSCs are investigated. It is found that the characteristic of the front electron transfer layer (ETL)/perovskite interface has a significant influence on the performance of PSCs than that of the back perovskite/hole transfer layer (HTL) interface. Additionally, a PCE of 15.05% with a high open-circuit voltage (VOC) of 1.54 V is obtained for the PSCs with FTO/ZnOS/CsPbIBr2/CuAlO2/Au structure. Finally, two-terminal monolithic all-perovskite double-junction tandem solar cells (TSCs) with the architecture of FTO/ZnOS/CsPbIBr2/CuAlO2/ITO/TiO2/MAPbI3/Spiro-MeOTAD/Au are constructed, and a maximum PCE of 27.4% (VOC of 2.60 V, JSC of 12.21 mA/cm2, and FF of 86.42%) is obtained for the TSCs with top and bottom absorber thicknesses of 600 nm and 500 nm respectively. Furthermore, four-terminal triple-junction TSCs are designed with silicon solar cells as bottom sub-cell, and a maximum PCE of 35.35% is achieved. These results will provide theoretical guidance for the fabrication of high performance TSCs.

It is well known that the phase stability of CsPb(I1−xBrx)3 (0 ≤ x ≤ 1) perovskite materials is enhanced under humid environments with the increase of Br− concentration in film, however, the bandgap (Eg) is also widened synchronously, resulted in limiting the light harvesting and then reducing the power conversion efficiency (PCE) of devices. Hence, how to realize the compatibility of high stability and high PCE is a challenge for device based on CsPb(I1−xBrx)3. In this work, the two- (2-T) and four-terminal (4-T) tandem solar cells (TSCs) consisting of a CsPb(I1−xBrx)3 top sub-cell and a crystalline silicon (c-Si) bottom sub-cell are constructed and compared. It is found that in the case of 2-T configuration, performance of device is very sensitive to the Eg and the thickness of top sub-cell, and a maximum PCE of 29.23% is achieved only for the CsPbI3 top sub-cell at an optimum thickness of 275 nm. However, in the 4-T formation, devices present a weak dependence on the Eg and the thickness of top sub-cell, and PCEs above 28.5% can be obtained when CsPbBr3 is used as top sub-cell. These results highly underline the application potential of 4-T CsPb(I1−xBrx)3/Si TSCs, especially for CsPbBr3/Si TSC.

In recent years, inorganic CsPbBr3-based perovskites have accomplished considerable progress owing to their superior stability under harsh humid environment. The power conversion efficiency (PCE) of CsPbBr3 perovskite solar cells (PSCs) has seen an unprecedented development from 5.74% to 10.91% with the improvement of the CsPbBr3 crystal quality. Despite extensive research efforts, the device efficiency of the CsPbBr3-based PSCs still lags behind that of other hybrid perovskite materials. Therefore, there is a significant interest in further boosting the performance of all-inorganic CsPbBr3 PSCs by the synergic optimization of films and device interfaces. In this review, we have discussed and summarized recent advances and methodologies related to CsPbBr3 films and PSCs. Furthermore, we discuss different fabrication strategies such as solution-based and vapor-based methods and their influence on the properties of CsPbBr3, particularly the morphology of films. Moreover, the timeline of improvement of the device efficiency from 2015 to 2020 is comprehensively addressed and developments are clearly sorted out by addressing critical factors influencing the photovoltaic performance. We further highlight state-of-the-art engineering strategies for CsPbBr3 PSCs that facilitate the crystallization control, charge extraction, suppression of charge recombination, and defect passivation in a systematic manner. At the end of the review, the summary and perspectives are presented along with beneficial guidelines for developing highly efficient and stable CsPbBr3 PSCs.

Recently, inorganic perovskite solar cells (PSCs) based on CsPbBr3 have triggered incredible interest due to the demonstrated excellent stability against thermal and high humidity environmental conditions. However, the power conversion efficiency (PCE) of the CsPbBr3-based PSCs is still lower than that of the organic-inorganic hybrid one, because of the large band gap and serious charge recombination at the interface or inside the device. Here, the working mechanism of the devices with normal n-i-p planar structure is modeled and investigated using SCAPS 1D simulation software. The simulation results state that the proper band structure of PSCs is crucial to carrier separation and transport. The high interface recombination, originated from the large band offsets of the electron transport material (ETM)/absorber and absorber/hole transport material (HTM) respectively, can be effectively diminished with the continuous gradient junction design of the absorber, and a PCE of 11.58% is obtained with a high open-circuit voltage (VOC) of 1.68 V. Moreover, by building a heterojunction bilayer absorption scenario of CsPbIBr2/CsPbBr3 and employing ZnOS and Cu2ZnSnS4 films as the ETM and HTM respectively, the PCE of PSCs is further increased to 15.89%, caused mainly by the enhancement in short-current density (JSC). Moreover, reducing the interface defect density is also very important to improve the performance of PSCs. These results will provide theoretical guidance for improving the performance of the CsPbBr3-based PSCs.

Formamidinium tin iodide (FASnI3), as one promising Pb-free halide perovskite, has received extensive attention. But perovskite solar cells (PSCs) based on FASnI3 films have yet to realize the high power conversion efficiency (PCE) achieved in its Pb-based counterparts. To investigate the limitation of FASnI3-based perovskite solar cells with inverted p-i-n planar structures, the influences of various parameters on the device performance are analyzed through device simulation. The results reveal that defect density at front hole transport material (HTM)/absorber interface is critical for high efficiency. And it is interesting to note that the doping density, rather than the doping type and its space distribution, dominates the device properties, and an upper limit of 1 × 1016 cm−3 is achieved. In addition, the response of device to band offset is investigated, and an optimum electron affinity of 3.9 eV is obtained. Finally, the effects of relative permittivity and thickness of the absorber with different carrier lifetime are studied. A maximum PCE of 9.75% is achieved at absorber thickness of 300 nm with carrier lifetime of 0.1 ns? These results show that optimizing the interface property and band offset, improving the stability of Sn2+ and reducing the defect density of absorber layer are the main challenges for high-performance FASnI3-based PSCs in the future research.

Owing to the inevitability of moisture/thermal instability in organic-inorganic hybrid perovskites, pure inorganic perovskites such as CsPbI2Br perovskite have surfaced as promising options for commercial perovskite solar cells (PSCs) due to their high photovoltaic performance and excellent inherent stability. However, designing additive engineering approaches to mitigate defect-induced crystalline phase transitions from a photosensitive perovskite phase to a non-perovskite phase has been a difficult task for researchers. In this work, using a one-step spin coating approach, we have prepared a polyvinylpyrrolidone (PVP) polymer-incorporated stable phase of CsPbI2Br at a low temperature (120 ​°C). Examinations using structural, morphological, and photo-physical measurements revealed that the optimum amount of PVP can greatly improve the optoelectronic properties of the film, which facilitates in reducing the trap states and defect in perovskite film, thus enabling charge carrier separation and suppressing charge recombination. As a result, the device based on 5 ​mg-PVP achieves a champion power conversion efficiency (PCE) of 10.47%, with a fill factor (FF) of 56.35%, a short-circuit current (JSC) of 18.47 ​mA ​cm2, and an open-circuit voltage (VOC) of 1.01 ​V, which is significantly higher than the device without PVP (6.36%). These findings suggest that PVP-CsPbI2Br has tremendous promise for future research and application in photovoltaic devices.

In this paper, we present a successful partial substitution of PbI2 by a much less expensive and toxic FeCl2 in perovskite films, namely MAI(PbI2)1−x(FeCl2)x (MA = CH3NH3+), and the followed effects on the performance of planar heterojunction perovskite solar cells (PSCs). The incorporation of a small content of Fe and Cl ions into the perovskite films could improve the growth morphology, enhance the crystallinity, increase the carrier lifetimes, as well as tune the material work function and Fermi level without significantly changing the band gap. Consequently, by adjusting the FeCl2 substitution fraction into the perovskite films, a power conversion efficiency above 17% is achieved with a high open-circuit voltage up to 1.10 V. Our work implies that conventional chlorides as substituting material of PbI2 have huge potential for the fabrication of more ecological PSCs.

Due to its outstanding stability, all-inorganic cesium lead bromide (CsPbBr3) perovskite is gaining increasing attention as a functional material in photovoltaics and other optoelectronic applications. However, the preparation of high-quality CsPbBr3 films via solution processing remains a significant challenge due to the cesium precursor’s low solubility in common solvents. As a result, developing viable evaporation deposition strategies is critical for increasing the photovoltaic performance of perovskite solar cells (PSCs) based on CsPbBr3. In this paper, a modified hybrid chemical vapor deposition is applied to fabricate CsPbBr3 films, and the effects of reaction temperature and reaction time on the crystallinity, morphology, and photo-electric properties of the films are investigated. By optimizing the reaction conditions, high-quality CsPbBr3 films with good crystallinity and uniformity are successfully obtained. Based on these films, CsPbBr3 PSCs with a device configuration of fluorine-doped tin oxide/compact-TiO2/CsPbBr3/carbon attained impressive power conversion efficiency of 4.41% with an ultra-high open-circuit voltage (V OC) of 1.39 V. This demonstration suggests that the modified hybrid chemical vapor deposition strategy enables a promising fabrication route suitable for all-inorganic perovskite thin films in photovoltaic application.

Inorganic perovskites (CsPbX3, X = I−, Br− or Cl−) have got researchers attention in the photovoltaic community due to their exceptional photoelectric properties and high thermal stability. In this work, we have explained a two-step vapor deposition approach to fabricate the CsPbCl3 films. To improve the properties of CsPbCl3 perovskite, different reaction conditions and their influence on the structural, morphological and optical properties of resultant films were systematically examined. We found that the proposed deposition strategy has a wide reaction window and is viable for the preparation of uniform CsPbCl3 films. The optimal reaction conditions resulted in improved crystallinity, morphology and photoluminescence. The present work will provide beneficial guidance for high-quality CsPbCl3 and other CsPbX3 perovskite films for future optoelectronic applications.

Organic–inorganic hybrid perovskite solar cells have made great breakthroughs in the past few years, and spurred researchers to develop and experiment a variety of new architectures. One-dimensional nanostructures are naturally introduced in solar cells, because of their excellent charge transport properties and open-pore structure. However, the performances of these solar cells are inferior to their mesoporous counterparts, suggesting that some unique mechanisms maybe held behind devices operation. Here, a three-dimensional optical model combined with a two-dimensional axisymmetric semiconductor model is applied to investigate the influence of the architectural design of scaffolds on the properties of perovskite solar cells based on Al2O3 nanorod arrays. Simulation results show a great dependence of device performance on the density, length and porosity of Al2O3 nanorods, which decided the electron field distribution and carrier recombination loss inside the cells. Strikingly, an optimal length of 450 nm for Al2O3 nanorods is obtained for the perovskite solar cells with efficiency over 20% at porosity of 0.7. The results obtained have some guidance function on the fabrication of high efficiency PSCs based on nanorods.

Organo-metal halide perovskite solar cells have shown unique charms in the upgrade rate of maximum power conversion efficiency, the diversity of device architecture and facilitated fabrication process. And the clear understanding of the role of each component and the basic working mechanisms in solar cells is important for further improvement in efficiency, especially for mesoscopic perovskite solar cells. Here, a two-dimensional modeling of the TiO 2 nanowire-based organic–inorganic hybrid perovskite solar cells was performed combining the optical and electrical responses to reveal the impact of the properties of TiO 2 nanowire array and absorber layer. Simulation results show a great dependence of device performance on the electron concentration of TiO 2 nanowires, which decided the electron field distribution inside cells, and an optimum thickness of 600 nm is obtained for the TiO 2 nanowires with low electron concentration. The collection of carriers is primarily within perovskite itself, and the ratio through TiO 2 nanowire is less than 5%. These findings can facilitate device optimization and enhance the performance of the perovskite solar cells.

Recently, organo–metal halide perovskites have attracted much attention of the scientific community relating to their successful application in the absorber layer of low-cost solar cells. However, enough is known about the material and device properties, to realize that much remains to be learned. In this study, a two-dimensional modeling of planar heterojunction perovskite solar cells was performed combining the optical and electrical responses to reveal the impact of the carrier diffusion length, the relative permittivity of absorber layer and the valence band offset of absorber/hole transport material (HTM). Simulation results presented a great dependence of power conversion efficiency (PCE) on the carrier diffusion length of perovskite layer. Meanwhile, to achieve high PCE, the frequency depended dielectric constant should not exceeded 40 and the double HTMs design was very effective to match the valence bands between the absorber and HTM.

In recent years, the organic-inorganic perovskite materials have revolutionized the Photovoltaic industry with highly efficient power conversion devices accompanied by a high growth rate. However, these devices experience major environmental and stability issues that hinder their true potential. More recently, a rarely studied perovskite material Cs2SnI6 is gaining enormous attention due to its superior stability and suitable bandgap. In this work, we developed a modified two-step process to prepare uniform Cs2SnI6 films, and the influence of the reaction conditions on the properties is explored. The structural, morphological, optical, and electrical properties of the prepared films were investigated using x-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV–vis spectrometer, photoluminescence, and Hall Effect measurements, respectively. Phase stability and morphology of the films are improved with optimizing the reaction conditions. The results confirm the n-type semiconductor nature of Cs2SnI6 with bandgap ranging from 1.29 eV to 1.42 eV with maximum carrier mobility of 425 cm2 V−1 s−1. The present study will further provide potential research directions in improving the device efficiency of air-stable Cs2SnI6 perovskite solar cells.

Practicability of CsSnI3 has been limited by the lack of stability in humid environment. Here we calculated phase stability, the impact of H2O embedded in CsSnI3 and surface adsorption by the first-principles calculations. Total energy results show that γ-CsSnI3 and Y-CsSnI3 are more stable. However, the γ-CsSnI3 is hydrophilic-like and Y-CsSnI3 is hydrophobic-like. Further studies show that H2O tend to adsorb at the hollow sites on the (001) surface. The strong coupling between O and Cs atoms and hydrogen bonding render the deformation of (001) surface. These results are partially explained the phase instability of perovskites in air.

The morphology control of CH3NH3PbI3 (MAPbI3) thin-film is crucial for the high-efficiency perovskite solar cells, especially for their planar structure devices. Here, a feasible and effective post-treatment method is presented to improve the quality of MAPbI3 films by using methylamine (CH3NH2) vapor. This post-treatment process is studied thoroughly, and the perovskite films with smooth surface, high preferential growth orientation and large crystals are obtained after 10 s treatment in MA atmosphere. It enhances the light absorption, and increases the recombination lifetime. Ultimately, the power conversion efficiency (PCE) of 15.3% for the FTO/TiO2/MAPbI3/spiro-OMeTAD/Ag planar architecture solar cells is achieved in combination with this post-treatment method. It represents a 40% improvement in PCE compared to the best control cell. Moreover, the whole post-treatment process is simple and cheap, which only requires some CH3NH2 solution in absolute ethanol. It is beneficial to control the reaction rate by changing the volume of the solution. Therefore, we are convinced that the post-treatment method is a valid and essential approach for the fabrication of high-efficiency perovskite solar cells.

Recently, organo-metal halide perovskites have attracted much attention from the scientific community because of their successful application in the absorber layer of low-cost solar cells. For the further improvement of the performance of such cells, a thorough understanding of the influence of the material properties on the working mechanism of a device is very necessary and important. In this study, two-dimensional modeling of hole transport material free planar heterojunction solar cells was performed, in which electromagnetic simulation was directly linked to carrier transport calculations. An optimum absorber thickness of 200 nm was reproduced in the simulation at carrier diffusion length of 100 nm, in good agreement with previous experiments. This optimum thickness increased with the increase of diffusion length, and an efficiency of about 11% was obtained at 300 nm with a diffusion length of 300 nm. Finally, it was demonstrated that the relatively low efficiency of such solar cells was directly related to the low short-circuit photocurrent density (J SC) and the low open-circuit voltage (V OC) due to the insufficient absorption of the long-wavelength region and the nearly intrinsic doping concentration, respectively.