Tuning the Amount of Oxygen Vacancies in Sputter-Deposited SnOx films for Enhancing the Performance of Perovskite Solar Cells

This work demonstrates the effect of oxygen vacancies in SnOx thin films on the performance of perovskite solar cells. Various SnOx films with different amounts of oxygen vacancies were deposited by sputtering at different substrate temperatures (25-300 degrees C). The transmittance of the films decreased from 82 to 66% with increasing deposition temperature from 25 to 300 degrees C. Both X-ray photoelectron spectroscopy and electron-spin resonance spectroscopy confirmed that a higher density of oxygen vacancies was created within the SnOx film at a high substrate temperature, which caused narrowing of the SnOx bandgap from 4.1 (25 degrees C) to 3.74eV (250 degrees C). Combined ultraviolet photoelectron spectroscopy and UV/Vis spectroscopy showed an excellent conduction band position alignment between the methylammonium lead iodide perovskite layer (3.90eV) and the SnOx electron transport layer deposited at 250 degrees C (3.92eV). As a result, a significant enhancement of the open-circuit voltage from 0.82 to 1.0V was achieved, resulting in an increase of the power conversion efficiency of the perovskite solar cells from 11 to 14%. This research demonstrated a facile approach for controlling the amount of oxygen vacancies in SnOx thin films to achieve a desirable energy alignment with the perovskite absorber layer for enhanced device performance.