Study of the Degradation of PTB7-Th:PC70BM-based Solar Cells using TiOx as Electron Transport Layers under Ambient Environment

In this work, the degradation study of PTB7-Th:PC7oBM-based inverted organic solar cells (iOSCs) by impedance spectroscopy is presented. Titanium oxide (TiO
_x
) with an ultra-thin film thickness was used as electron transport layer (ETL). A high performance of the TiOx-based device is achieved with the power conversion efficiency (PCE) of up to 9.83% for the fresh device. To gain a better understanding to the effect of TiO
_x
as ETL on device performance and stability, a degradation measurement was performed on the nonencapsulated cells under ambient environment in the dark condition. This condition was chosen for the nonencapsulated devices in order to simulate a more realistic circumstance of degradation process over the storage time. The PCE of the nonencapsulated device decreased down to 90% of initial PCE after 70 h. The degradation causes of each layer inside of the device can be able to be identified by impedance spectroscopy.