Light-induced effects on Spiro-OMeTAD films and hybrid lead halide perovskite solar cells

摘要

Perovskite (PS) solar cells have emerged as a promising technology for low-cost and efficient photovoltaics.However, the main limiting factors are related to their low long-term stability. The loss ofperformance of these devices is commonly attributed to degradation of the PS itself. In order to furtherexplore the origins of such limited stability, we have developed UV–vis spectroscopy studies that clearlydemonstrate that PS layers remain unalterable under the working conditions. On the contrary, significantvariations in the absorption spectra of the Spiro-OMeTAD layer (Spiro), a commonly used hole transportingmaterial (HTM), indicate that the loss of performance over the irradiation time are attributed tothe degradation of Spiro. UV–vis measurements evidence a photo-induced oxidation of Spiro, both underair and inert atmosphere. This photo-oxidation is accelerated by the commonly employed additives ofthe Spiro (LiTFSI and tBP), as well as by the interfacial contact with the electron injecting layer (TiO2).Therefore, our results point to the Spiro degradation as the main mechanism that induces the limitedfunctioning of the PS solar cells. Consequently, focusing on the development of alternative HTMs stableunder the working conditions is one of the critical issues to be overcome for a suitable progress of PSsolar cells and related opto-electronic devices.