Enhancing the Power Conversion Efficiency of Perovskite Solar Cells through Interface Passivation with a Novel Organic Halide Salt

Abstract

Perovskite solar cells (PSCs) exhibit an exceptional capacity for high efficiency in the conversion of solar energy, however, due to nonradiative recombination losses at charge transport interfaces, primarily between the perovskite and hole transport layer (HTL), PSC commercialization has been challenged by both efficiency and long-term stability. In this study, we prepare an organic halide salt, 4(trifluoromethyl) phenethyl ammonium iodide (CF₃PEAI), and utilize it as an interfacial passivation layer in planar n-i-p PSCs. CF₃PEAI is deposited via spin-coating prior to HTL deposition onto the  perovskite film. Complete characterization of the CF₃PEAI passivated devices via J–V measurements, TRPL, EIS, and SCLC indicates that CF₃PEAI effectively binds to uncoordinated Pb²⁺ sites thereby preventing trap assisted recombination as well as improving energy level alignment with Spiro OMeTAD. Consequently, the optimized devices yield a champion power conversion efficiency of 23.6% (22.4% average) and an approximate increase in efficiency of 5.5% when compared to unpassivated controls (18.2%). The voltage across the open circuit has increased from 1,076 V to 1,160 V, the fill factor has increased from 74.9% to 82.8%, and the hysteresis index has decreased from 11.7% to 2.9%. Also, the passivation by CF₃ PEAI has increased the operational lifetime () of the solar cells exposed to continuous light from 210 h to 620 h. The presence of the trifluoromethyl group provides a high degree of hydrophobicity and will create a dipole effect, which enhances the extraction of charges. The results have shown that the use of fluorinated organic halide salts can provide a simple and effective means to enhance both the efficiency and the stability of solar cells; thereby providing a framework for the development of future passivating materials.