Enhancing Charge Carrier Transport in the Carbon-Electrode-Based CsPbI2Br Perovskite Solar Cells via I/Br Homogenization Process Modulation and Oleic Acid Surface Passivation

The carbon-electrode-based CsPbI2Br perovskite solar cells (C-PSCs) are promising photovoltaic technology because of their enhanced stability and low cost. However, the CsPbI2Br film suffers from uneven surface morphology with stripes and the defect-rich surface, which are detrimental to the charge carrier transport between perovskite and carbon. Here, we demonstrate that the formation of stripes is directly related to the I/Br homogenization process during annealing. By introducing a pre-annealing treatment before high temperature annealing, the I/Br homogenization process is modulated and the stripe is successfully wiped off. Besides, enhanced charge carrier transport in the C-PSCs is achieved. Oleic acid (OA) is then introduced to modify the stripe-free perovskite film surface. It is revealed that the carboxyl group in the OA molecule can passivate the undercoordinated Pb ions, leading to further improved charge carrier transport. Eventually, a power conversion efficiency (PCE) of 15.57% is achieved, which is among the highest PCE for the CsPbX3-based C-PSCs. This work demonstrates that combining surface planarization with surface passivation is an effective strategy for developing highly efficient C-PSCs.