Printable Low‐Temperature Carbon for Highly Efficient and Stable Mesoscopic Perovskite Solar Cells

Carbon‐based perovskite solar cells (C‐PSCs) have attracted worldwide attention in the research community due to their low‐cost fabrication and improved stability compared with conventional PSCs. However, the cell reproducibility and inconsistency of perovskite infiltration into micrometer‐thick mesoscopic devices remain an issue for cell fabrication. Furthermore, full perovskite crystallization in the screen‐printed device without any perovskite formed on the mesoporous carbon electrode is always challenging. The presence of protruding perovskite crystals on C‐PSCs is found, which initially leads to the hydrolysis of perovskites under humid condition and eventually accelerates the degradation. Herein, a low‐temperature (low‐T) carbon layer is incorporated through a scalable screen‐printing technique on top of C‐PSCs. C‐PSCs coated with low‐T carbon show good moisture (70% relative humidity) and thermal (65 and 85 °C) stability over 3,250 and 1,000 h, respectively, without any physical encapsulation. The device also shows high stability under continuous illumination at its maximum power point for 175 h. This hydrophobic and conductive carbon layer not only protects the exposed perovskite crystals from moisture but also enhances the photovoltaic performance of C‐PSCs with major fill factor and open‐circuit voltage improvement.