Interface Engineering of Perovskite Solar Cells with Air Plasma Treatment for Improved Performance

For high-efficiency perovskite solar cells (PSCs), interface engineering becomes critical for carrier collection from the active perovskite material to the transport layer. To enhance the power conversion efficiency (PCE), herein we demonstrate a novel method named surface plasma treatment on a mesoporous TiO₂ electron-transport layer (ETL) to improve electron extraction and transport properties at the perovskite/TiO₂ interface. According to the XPS results, the plasma treatment induced a partial reduction of Ti⁴⁺ to Ti³⁺ within the TiO₂ lattice and increased the concentration of oxygen vacancies on the TiO₂ surface. Ultraviolet photoelectron spectra (UPS) show that the Fermi level of TiO₂ upshifts about 0.2 eV which may effectively promote carrier separation and transfer at the perovskite/TiO₂ interface. In addition, these created donor levels of Ti³⁺ and oxygen vacancies donate extra electrons, increasing the conductivities of TiO₂ films and which could further promote transport. The time-resolved photoluminescence spectra (TRPL) confirm that the decay time decreases dramatically from 656 ns to 235 ns after 90 s plasma treatment, which indicates a more efficient electron-transfer process. Based on all the above-mentioned results, a remarkable enhancement in cell efficiency was obtained, such that the average efficiency was improved from 11.5 % to 14.3 % under AM 1.5G irradiation (100 mW cm^-2 ).