A Solution-Processed Dopant-Free Tin Phthalocyanine (SnPc) Hole Transport Layer for Efficient and Stable Carbon-Based CsPbI₂Br Planar Perovskite Solar Cells Prepared by a Low-Temperature Process

Carbon-based inorganic CsPbX3 (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 CsPbX3 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 CsPbI2Br 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 CsPbI2Br/carbon interface. This work provides a low-temperature and solution-processed method to fabricate the efficient and stable carbon-based inorganic PSCs.