In this work, planar inorganic perovskite solar cells (PSCs) with the simple structure of glass/ITO/SnO2/CsPbI2Br/C have been fabricated.

Solution‐processed nickel oxide nanocrystals (NiOx NCs) ink can be facilely applied to deposit NiOx thin films as the hole transport layer (HTL) for perovskite solar cells (PSCs). Both the efficiency and stability of the corresponding PSCs depend significantly on the size and the energy levels of the as‐synthesized NiOx NCs; however, previous studies have shown that these two aspects can be hardly controlled synchronously to maximize the device performance. Herein, a novel synthesis of highly dispersed NiOx NCs is demonstrated by employing tetraalkylammonium hydroxides (TAAOHs, alkyl = methyl, ethyl, propyl, butyl) as precipitating bases, where the varied alkyl chain lengths of TAAOHs enable the size control of the NiOx NCs and the subsequent altering of their Ni3+ contents, leading to tunable energy levels of the NiOx thin films. With the longest butyl chain, the smallest crystal size and the optimal energy level alignment at the NiOx/perovskite interface are achieved. After further passivating the detrimental Ni3+ species on the surface of NiOx HTL, a remarkable power conversion efficiency (PCE) approaching 23% is obtained, which is one of the highest PCEs reported for NiOx‐based inverted PSCs. Furthermore, the unencapsulated device exhibits excellent ultraviolet stability, which maintains ≈87% of its PCE after 200 h exposure.

Carbon‐based perovskite solar cells (PSCs) have gathered much attention due to their excellent thermal stability and low cost. However, the typically used hole‐conductor‐free PSCs based on carbon electrodes show the worst performance due to the serious charge recombination at the perovskite/carbon interface. In this work, the efficient and stable carbon‐based CsPbI2Br PSCs using Co3O4 as the hole transport material (HTM) are fabricated and their photoelectric properties are systematically investigated. It is found that the Co3O4 inorganic HTM effectively promotes photo‐generated charges separation and extraction, and suppresses charge recombination at the CsPbI2Br/carbon electrode interface, resulting in the improved photovoltaic performance. At the optimal Co3O4 concentration, the carbon‐based CsPbI2Br PSCs achieve the maximum efficiency of 11.21% with a negligible J–V hysteresis. This work provides a novel strategy to fabricate efficient and stable all‐inorganic PSCs.

Carbon-based inorganic CsPbX 3 (X = I, Br, Cl) perovskite solar cells (PSCs) are attracting great attention in the photovoltaic field because of their low cost, simple process, and superior thermal stability. However, the large difference in energy band between the CsPbX 3 and carbon electrode leads to the poor hole extraction and unfavorable charge recombination, thus deteriorating device's efficiency. In this work, a solution-processed dopant-free tin phthalocyanine (SnPc) film is used as a hole-transport layer (HTL) to fabricate carbon-based CsPbI 2 Br PSCs by a low-temperature process. At the optimal process, the device achieves a maximum efficiency of 11.39% with less hysteresis, which is much higher than 9.22% of reference device without the SnPc HTL. Moreover, the unencapsulated device exhibits the improved stability and remains about 90% of its initial efficiency after 30 days in ambient air (20−25 °C) with 25−35% relative humidity (RH). This finding reveals that the solution-processed dopant-free SnPc HTL can significantly promote charge transport and suppress charge recombination at the CsPbI 2 Br/carbon interface. This work provides a low-temperature and solutionprocessed method to fabricate the efficient and stable carbon-based inorganic PSCs.