Self-Assembled Benzotriazole Interlayer Stabilizes ZnO/Polymer Interfaces Enables Thermally Robust Organic Solar Cells

Improving the thermal stability of organic solar cells (OSCs) is essential for advancing their practical deployment. In this paper, the thermal stability of organic solar cells was significantly improved by a benzotriazole (BTA) molecular layer assembled at the ZnO/active layer interface, introduced by spin-coating on the polymer blend surface. Experimental results demonstrated that BTA modification effectively suppressed the diffusion of MoO₃ and its interaction with ZnO, thereby mitigating energy-level mismatch and interfacial recombination. Remarkably, the BTA-modified device retained 86% of its initial efficiency following prolonged thermal aging at 85 °C for 1000 h, compared to 70% for unmodified devices. Detailed analysis via X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) revealed that BTA reduced adsorbed oxygen content on ZnO and lowered its work function, facilitating improved charge transport. This study provides a solution-processable interfacial engineering strategy for enhancing OSC stability under practical operating conditions.