Tuning Hole Transport Layer using Urea for High-Performance Perovskite Solar Cells

Interface engineering is critical to the development of highly efficient perovskite solar cells. Here, urea treatment of hole transport layer (e.g., poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS)) is reported to effectively tune its morphology, conductivity, and work function for improving the efficiency and stability of inverted MAPbI₃ perovskite solar cells (PSCs). This treatment has significantly increased MAPbI₃ photovoltaic performance to 18.8% for the urea treated PEDOT:PSS PSCs from 14.4% for pristine PEDOT:PSS devices. The use of urea controls phase separation between PEDOT and PSS segments, leading to the formation of a unique fiber-shaped PEDOT:PSS film morphology with well-organized charge transport pathways for improved conductivity from 0.2 S cm⁻¹ for pristine PEDOT:PSS to 12.75 S cm⁻¹ for 5 wt% urea treated PEDOT:PSS. The urea-treatment also addresses a general challenge associated with the acidic nature of PEDOT:PSS, leading to a much improved ambient stability of PSCs. In addition, the device hysteresis is significantly minimized by optimizing the urea content in the treatment.