To fabricate efficient formamidinium tin iodide (FASnI3) perovskite solar cells (PSCs), it is essential to deposit uniform and dense perovskite layers and reduce Sn4+ content. Here we used solvent-engineering and nonsolvent dripping process with SnF2 as an inhibitor of Sn4+. However, excess SnF2 induces phase separation on the surface of the perovskite film. In this work, we report the homogeneous dispersion of SnF2 via the formation of the SnF2–pyrazine complex. Consequently, we fabricated FASnI3 PSCs with high reproducibility, achieving a high power conversion efficiency of 4.8%. Furthermore, the encapsulated device showed a stable performance for over 100 days, maintaining 98% of its initial efficiency.

　Beneficial effects are demonstrated by PbI2 incorporated into perovskite materials as a light absorber in solar cells. The PbI2 distributed into the perovskite layers leads to reduced hysteresis and ionic migration, and enables the fabrication of remarkably improved solar cells with a certified power conversion efficiency of 19.75% under air-mass 1.5 global (AM 1.5G) illumination of 100 mW cm−2 intensity.

　The improved performance achieved by combining tert-butyl copper (II) phthalocyanine (CuPC) and po-spiro-OMeTAD as hole transporting material (HTM) for formamidinium lead iodide (FAPbI3)-based perovskite solar cells is reported. A device efficiency of 19.4% under standard 1 sun is obtained.

　Highly transparent and nanostructured nickel oxide (NiO) films through pulsed laser deposition are introduced for efficient CH3NH3PbI3 perovskite solar cells. The (111)-oriented nanostructured NiO film plays a key role in extracting holes and preventing electron leakage as hole transporting material. The champion device exhibits a power conversion efficiency of 17.3% with a very high fill factor of 0.813.

　Most efforts to grow superior films of organic-inorganic perovskites for solar cells have focused on methylammonium lead iodide (MAPbI3). However, formamidinium lead iodide (FAPbI3) has a broader solar absorption spectrum that could ultimately lead to better performance. Yang et al. grew high-quality FAPbI3 films by starting with a film of lead iodide and dimethylsulfoxide (DMSO) and then exchanging the DMSO with formamidinium iodide. Their best devices achieved power conversion efficiencies exceeding 20%.

　Of the many materials and methodologies aimed at producing low-cost, efficient photovoltaic cells, inorganic–organic lead halide perovskite materials1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17 appear particularly promising for next-generation solar devices owing to their high power conversion efficiency. The highest efficiencies reported for perovskite solar cells so far have been obtained mainly with methylammonium lead halide materials1,2,3,4,5,6,7,8,9,10. Here we combine the promising—owing to its comparatively narrow bandgap—but relatively unstable formamidinium lead iodide (FAPbI3) with methylammonium lead bromide (MAPbBr3) as the light-harvesting unit in a bilayer solar-cell architecture13. We investigated phase stability, morphology of the perovskite layer, hysteresis in current–voltage characteristics, and overall performance as a function of chemical composition. Our results show that incorporation of MAPbBr3 into FAPbI3 stabilizes the perovskite phase of FAPbI3 and improves the power conversion efficiency of the solar cell to more than 18 per cent under a standard illumination of 100 milliwatts per square centimetre. These findings further emphasize the versatility and performance potential of inorganic–organic lead halide perovskite materials for photovoltaic applications.

　Efficient metal-oxide-free perovskite solar cells were successfully developed by employing the N–I–P architecture. The modified solvent engineering process employing a diethylether drip as an orthogonal solvent enabled fabrication of a multi-layered device comprising FTO/PEI/PCBM/MAPbI3/PTAA/Au at low temperature (≤100 °C). Optimization of the thickness of the phenyl-C61-butyric acid methyl ester (PCBM) layer in the planar device yielded an overall power conversion efficiency (PCE) of 15.3% with a large hysteresis but a steady-state efficiency of 13.9% under AM 1.5G 100 mW cm−2 illumination. The use of the low-temperature processed dense-TiO2 layer in conjunction with the PCBM layer gave rise to performance comparable to that of the single electron transport layer (ETL) device and enabled fabrication of an efficient, flexible perovskite solar cell with a PCE of 11.1%.

　Highly efficient p–i–n perovskite solar cells employing a flat and thick CH3NH3PbI3 film and a thin PCBM film are fabricated by the solution-process at low temperature. Through attainment of optimized PCBM thickness and insertion of the LiF interlayer, the unit cell shows 14.1% of overall power conversion efficiency (PCE) with a Jsc of 20.7 mA cm−2, a Voc of 0.866 V, and a FF of 78.3% under AM 1.5G 100 mW cm−2 conditions, while a larger area 10 cell serially connected module (10 × 10 cm2) shows an 8.7% PCE. These PCE values are the highest reported to date for the planar perovskite–PCBM solar cells.

　Besides the generated photocurrent as a key factor that impacts the efficiency of solar cells, the produced photovoltage and fill factor are also of critical importance. Therefore, understanding and optimization of the open-circuit voltage (Voc) of perovskite solar cells, especially with an architecture consisting of mesoporous (mp)-TiO2/perovskite/hole transporting materials (HTMs), are required to further improve the conversion efficiency. In this work, we study the effects of the energy level between CH3NH3(= MA)PbI3 and MAPbBr3 and a series of triarylamine polymer derivatives containing fluorene and indenofluorene, which have different highest occupied molecular orbital (HOMO) levels, in terms of the photovoltaic behaviour. The voltage output of the device is found to be dependent on the higher energy level of perovskite solar absorbers as well as the HOMO level of the HTMs. The combination of MAPbBr3 and a deep-HOMO HTM leads to a high photovoltage of 1.40 V, with a fill factor of 79% and an energy conversion efficiency of up to 6.7%, which is the highest value reported to date for MAPbBr3 perovskite solar cells.

　Three spiro-OMeTAD derivatives have been synthesized and characterized by 1H/13C NMR spectroscopy and mass spectrometry. The optical and electronic properties of the derivatives were modified by changing the positions of the two methoxy substituents in each of the quadrants, as monitored by UV–vis spectroscopy and cyclic voltammetry measurements. The derivatives were employed as hole-transporting materials (HTMs), and their performances were compared for the fabrication of mesoporous TiO2/CH3NH3PbI3/HTM/Au solar cells. Surprisingly, the cell performance was dependent on the positions of the OMe substituents. The derivative with o-OMe substituents showed highly improved performance by exhibiting a short-circuit current density of 21.2 mA/cm2, an open-circuit voltage of 1.02 V, and a fill factor of 77.6% under 1 sun illumination (100 mW/cm2), which resulted in an overall power conversion efficiency (PCE) of 16.7%, compared to ∼15% for conventional p-OMe substituents. The PCE of 16.7% is the highest value reported to date for perovskite-based solar cells with spiro-OMeTAD.

　We report on the fabrication of PbS/CH3NH3PbI3 (=MAP) core/shell quantum dot (QD)-sensitized inorganic–organic heterojunction solar cells on top of mesoporous (mp) TiO2 electrodes with hole transporting polymers (P3HT and PEDOT:PSS). The PbS/MAP core/shell QDs were in situ-deposited by a modified successive ionic layer adsorption and reaction (SILAR) process using PbI2 and Na2S solutions with repeated spin-coating and subsequent dipping into CH3NH3I (=MAI) solution in the final stage. The resulting device showed much higher efficiency as compared to PbS QD-sensitized solar cells without a MAP shell layer, reaching an overall efficiency of 3.2% under simulated solar illumination (AM1.5, 100 mW·cm–2). From the measurement of the impedance spectroscopy and the time-resolved photoluminescence (PL) decay, the significantly enhanced performance is mainly attributed to both reduced charge recombination and better charge extraction by MAP shell layer. In addition, we demonstrate that the MAP shell effectively prevented the photocorrosion of PbS, resulting in highly improved stability in the cell efficiency with time. Therefore, our approach provides method for developing high performance QD-sensitized solar cells.

　A facile and innovative method for the fabrication of highly fluorescent micro-patterns is presented, which operates on the principle of phototriggered phase transition and physical mass migration in the crystalline film of a cyanostilbene-type aggregation-induced enhanced emission (AIEE) molecule ((Z)-2,3-bis(3,4,5-tris(dodecyloxy)phenyl) acrylonitrile) with liquid-crystalline (LC) mesomorphic behavior.