Performance improvement of perovskite solar cells by employing a CdSe quantum dot/PCBM composite as an electron transport layer

Organic–inorganic hybrid perovskites have recently attracted considerable interest for application in solar cells due to their low cost, high absorption coefficient and high power conversion efficiency (PCE). Herein, we utilize a CdSe quantum dot/PCBM composite as an electron transport layer (ETL) to investigate the structure, stability and PCE of CH₃NH₃PbI_3−xCl_x perovskite solar cells. It is found that adsorption of the CdSe/PCBM composite reduces the roughness of the perovskite, leading to a high-quality film with a compact morphology. Density functional theory (DFT) based first-principles calculations show that CdSe enhances the chemical stability of CH₃NH₃PbI_3−xCl_x involving strong atomic orbital hybridization. Interestingly, an inorganic-terminated perovskite surface has much stronger interaction with CdSe compared to the surface with organic CH₃NH₃ termination, with noticeable interfacial charge redistribution. Experiments on solar cells incorporating the CdSe/PCBM composite as the ETL show enhanced photocurrent and fill factor, which is related to the in-built electric field between CH₃NH₃PbI_3−xCl_x and CdSe that greatly facilitates the separation of electron and hole pairs. We show an improved PCE of 13.7% with enhanced device stability in a highly humid atmosphere. These joint theoretical–experimental results may provide a new aspect for improving the structural stability and operating performance of optoelectronic devices based on perovskite structures.