Designing new fullerene derivatives as electron transporting materials for efficient perovskite solar cells with improved moisture resistance

A new fullerene derivative named C5-NCMA is introduced as an electron transporting material (ETM) to replace the commonly used PCBM in the planar p-i-n perovskite solar cells (PVSCs). Compared with PCBM, this fullerene derivative features a higher hydrophobicity, higher LUMO energy level and higher ability of self-assembly. With the device structure of FTO/NiO_x/MAPbI₃/ETM/Ag, the C5-NCMA showed power conversion efficiency (PCE) of up to 17.6% with negligible hysteresis, which is higher than PCBM (16.1%). It was found that a higher LUMO energy level was obtained for C5-NCMA compared to PCBM, which favored a higher open-circuit voltage (V_oc) in PVSCs with C5-NCMA than PCBM. Besides, the higher electron mobility, photoluminescence (PL) quenching efficiency and quenching rate of C5-NCMA led to more efficient electron transport and charge extraction in the device, thus resulting in a higher fill factor (0.79). Most importantly, the stability of PVSCs to moisture is significantly enhanced for C5-NCMA compared to PCBM due to the hydrophobic nature of C5-NCMA. Thus, we believe that the present work provides an important guide for the further development of ETMs for stable and efficient PVSCs.