High‐Efficiency Carbon‐Based CsPbIBr2 Solar Cells with Interfacial Energy Loss Suppressed by a Thin Bulk‐Heterojunction Layer

The CsPbIBr 2 perovskite has obvious advantages in balancing the stability and efficiency in inorganic perovskite solar cells (PSCs). Its large bandgap of 2.08 eV, which leads to a narrow spectral absorption (<600 nm), is the key limit to yielding a high power conversion efficiency (PCE). Herein, it is demonstrated that by integrating a thin bulk‐heterojunction (BHJ) layer (19 nm) composed of the typical poly (3‐hexylthiophene‐2,5‐diyl) and [6,6]‐phenyl methyl C61 butyric acid methyl ester (P3HT:PCBM) with CsPbIBr 2 perovskite, a carbon‐based all‐inorganic PSC achieves a much higher champion PCE (11.54%) than the original CsPbIBr 2 device (8.87%), and the value is also at the highest PCE level of all‐inorganic CsPbIBr 2 PSCs. The integration of a thin BHJ layer brings an expanded light absorption range, better charge transfer dynamics, suppressed interfacial energy loss, and improved long‐term stability. The unencapsulated CsPbIBr 2 PSC with an integrated BHJ layer shows excellent long‐term stability in an ambient atmosphere with high relative humidity (RH ≈ 45%, T ≈ 25 °C). Therefore, the BHJ integration is an effective strategy on the road to industrialization of carbon‐based all‐inorganic PSCs with low cost, high efficiency, and excellent long‐term stability.