Mechanism and Analysis of Thermal Burn-In Degradation of OPVs Induced by Evaporated HTL

In this study, we focus on the analysis of thermal burn-in degradation behavior of organic photovoltaics (OPVs) at 85 °C under nitrogen atmosphere. In this thermal aging as the accelerated test, the thermal burn-in loss (initially rapid drop) in the power conversion efficiency (PCE) of the inverted OPV devices based on ITO/ZnO/PTB7:PC ₇₁ BM/MoO ₃ /Ag was shown over 40% PCE reduction. We systematically investigate the effects of bulk heterojunction structure and Ag electrode on thermal degradation. Moreover, we adopt two device architectures to investigate the effect of contact between the charge carrier transport layer and active layer on thermal burn-in loss. The degradation mechanism and origin of thermal burn-in loss induced by the evaporated MoO ₃ molecules or charge traps are proposed for the first time. The impedance analysis was conducted to verify the mechanism. Insight into the burn-in mechanism will be helpful for developing OPV fabrication strategies and designs to effectively reduce the thermal burn-in loss. The conventional OPV with the structure of ITO/MoO ₃ /PTB7:PC ₇₁ BM/ZnO/Ag remains ~94% of its initial PCE after 500 h of thermal aging at 85 °C.