Improved longtime stability of highly efficient polymer solar cells by accurately self-formed metal oxide interlayer at metal electrode

Abstract Al as a cheap and air-stable metal material has been widely applied to polymer solar cells (PSCs) as an efficient electrode. However, there are few care whether Al is a right electrode in PSCs for longtime stability. The inverted PSCs with the structure of ITO/ZnO/PTB7-Th:PC 71 BM/MoO 3 /Metal electrode were fabricated and the performance and stability of inverted PSCs with Al and AgAl electrodes were investigated. PSCs with AgAl electrode got the highest PCE value of 9.3% without aging. While the PCE of PSCs with Al electrode can be gradually improved and reach the highest value of 7.8% after aging for 36 h, which is attributed to the formation of AlO x interlayer at the interface of MoO 3 /Al. PSCs with AgAl electrode still retained 69% of the initial PCE value and got 6.6% of PCE aging for 796 days, showing amazing stability. However, PSCs with Al electrode was dropped to 3.7% of PCE aging for 796 days due to the continuously increased thickness of AlO x interlayer, which can greatly increase the series resistance of cells. PSCs with AgAl electrode can be further improved and reach 10.2% of PCE using AZO (Al doped ZnO) instead of ZnO and show better UV-light resistance. The enhanced stability of PSCs with AgAl electrode is attributed to the dense and limited thick AlO x interlayer self-formed at the MoO 3 /AgAl interface due to the low content of Al. Our results demonstrated that Ag alloy electrode such as AgAl is a good strategy to accurately control the thickness of the metal oxidation interlayer, which can overcome the disadvantage of Al electrode and greatly improve the longtime stability of devices.