Degradation analysis of inverted PM6 (PBDB-T-2F):Y7 (BTP-4CI) solar cells with PDINO and MoO3 as the ETL/HTL

Abstract

In this work, an analysis is presented of both the degradation and the photo-degradation of inverted organic solar cells (iOSCs), with the PM6 (PBDB-T-2F):Y7 (BTP-4Cl) blend without any additive as the active layer. PDINO and MoO₃ are used as electron and hole transport layers (ETL/HTL), respectively. The maximum obtained power conversion efficiency (PCE) of the devices is 9.14%. The long-term operational stability and the photostability aging tests of the unencapsulated iOSCs under continuous exposure of AM 1.5G illumination conditions (100 mW cm⁻²) are performed under dark and nitrogen environments for 3552 h, and following the ISOS-L-1 protocols for 220 h. The times to reach 90%, 80%, and 50% of the initial PCE of the iOSCs (T₉₀, T₈₀, and T₅₀) under dark and N₂ conditions are 2363 h, 2918 h, and >3552 h, respectively, and 17 h, 31 h, and 220 h, respectively, under ISOS-L-1. The analysis showed that V_OC is the least affected parameter by the degradation for both studies. The impedance spectroscopy (IS) measurements confirmed that the PDINO layer degradation was the main cause of degradation of the devices under dark and nitrogen environments, while the active layer showed the best stability. On the other hand, following the ISOS-L-1 protocols under continuous illumination, the IS results suggest that the performance degradation of iOSCs is mainly due to the photo-degradation of both the active and the PDINO layers, while the MoO₃ layer showed the best stability.