Preparation of black formamidinium lead iodide (FAPbI3) requires high temperature annealing and the incorporation of smaller A-site cations, such as methylammonium (MA+), cesium or rubidium. A major advantage of vacuum processing is the possibility to deposit perovskite films at room temperature (RT), without any annealing step. Here we demonstrate stabilization of the cubic perovskite phase at RT, in a three-sources co-sublimation method. We found that the MA+ incorporation is a selflimiting process, where the amount of MA+ which is incorporated in the perovskite is essentially unvaried with increasing MAI deposition rate. In this way a phase-pure, cubic perovskite with a bandgap of 1.53 eV can be obtained at room temperature. When used

Herein, the long‐term stability of vacuum‐deposited methylammonium lead iodide (MAPbI3) perovskite solar cells (PSCs) with power conversion efficiencies (PCEs) of around 19% is evaluated. A low‐temperature atomic layer deposition (ALD) Al2O3 coating is developed and used to protect the MAPbI3 layers and the solar cells from environmental agents. The ALD encapsulation enables the MAPbI3 to be exposed to temperatures as high as 150 °C for several hours without change in color. It also improves the thermal stability of the solar cells, which maintain 80% of the initial PCEs after aging for ≈40 and 37 days at 65 and 85 °C, respectively. However, room‐temperature operation of the solar cells under 1 sun illumination leads to a loss of 20% of their initial PCE in 230 h. Due to the very thin ALD Al2O3 encapsulation, X‐ray diffraction can be performed on the MAPbI3 films and completed solar cells before and after the different stress conditions. Surprisingly, it is found that the main effect of light soaking and thermal stress is a crystal reorientation with respect to the substrate from (002) to (202) of the perovskite layer, and that this reorientation is accelerated under illumination.

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The electron-transporting layer (ETL) material is one of the critical components of the n-i-p planar perovskite solar cells (PSCs). TiO2 is the most typically used ETL material; however, low electron mobility and conductivity of TiO2 limit the performance of the cells. Ion doping is an effective method for improving the electrical properties of TiO2 films. In this study, pure and tantalum (Ta)-doped TiO2 films, fabricated with the spray pyrolysis method, were employed as the ETL in the n-i-p planar PSCs. Ta doping improved the electrical conductivity and decreased interface defect between the TiO2 electron transport and perovskite layers, promoting efficient electron transfer at the interface. After dopant optimization of transport layers, the overall power conversion efficiency was increased to as high as 20.45% with negligible hysteresis exceeding the previous highest efficiency recorded for Ta-doped TiO2 ETL-based PSCs. More importantly, Ta-doped TiO2 ETL-based PSCs exhibited an admissible photostability under continuous illumination including UV radiation and retained 65% of their initial efficiency over 300 h in the ambient environment, higher than that of 50% for the control device. These findings indicated that spray-pyrolyzed Ta-doped TiO2 films could be a promising compact layer to fabricate highly efficient and UV-stable planar PSCs in large-scale manufacturing.

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p–n heterostructured photocatalysts consisting of hydrothermally derived CuCrO2 nanoparticles and electrospun SnO2 nanofibers were successfully prepared for the first time.

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Herein, we have demonstrated n–i–p PSCs with an efficiency of 22.45% and high thermal stability using dopant-free 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) as the solution-processed hole transporting layer (HTL).