γ‐Ray Irradiation Enables Annealing‐ and Light‐Soaking‐Free Solution Processable SnO2 Electron Transport Layer for Inverted Organic Solar Cells

Abstract The electrode buffer layer is crucial for high‐performance and stable OSCs, optimizing charge transport and energy level alignment at the interface between the polymer active layer and electrode. Recently, SnO 2 has emerged as a promising material for the cathode buffer layer due to its desirable properties, such as high electron mobility, transparency, and stability. Typically, SnO 2 nanoparticle layers require a postannealing treatment above 150°C in an air environment to remove the surfactant ligands and obtain high‐quality thin films. However, this poses challenges for flexible electronics as flexible substrates can't tolerate temperatures exceeding 100°C. This study presents solution‐processable and annealing‐free SnO 2 nanoparticles by employing y‐ray irradiation to disrupt the bonding between surfactant ligands and SnO 2 nanoparticles. The SnO 2 layer treated with y‐ray irradiation is used as an electron transport layer in OSCs based on PTB7‐Th:IEICO‐4F. Compared to the conventional SnO 2 nanoparticles that required high‐temperature annealing, the y‐SnO 2 nanoparticle‐based devices exhibit an 11% comparable efficiency without postannealing at a high temperature. Additionally, y‐ray treatment has been observed to eliminate the light‐soaking effect of SnO 2 . By eliminating the high‐temperature postannealing and light‐soaking effect, y‐SnO 2 nanoparticles offer a promising, cost‐effective solution for future flexible solar cells fabricated using roll‐to‐roll mass processing.