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

[Display omitted] •Self-formed AlOx at Al/MoO3 interface improve built-in field of polymer solar cells.•Too Thick AlOx increase Rs, which reduce efficiency and stability of Al based cells.•Thickness of AlOx interlayer self-formed at AgAl/MoO3 interface can be controlled.•Dense and right thick AlOx improve PCE and longtime stability of AgAl based PSCs.•AZO instead of ZnO as ETL helps to improve efficiency and UV-resistance of PSCs. 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:PC71BM/MoO3/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 36h, which is attributed to the formation of AlOx interlayer at the interface of MoO3/Al. PSCs with AgAl electrode still retained 69% of the initial PCE value and got 6.6% of PCE aging for 796days, showing amazing stability. However, PSCs with Al electrode was dropped to 3.7% of PCE aging for 796days due to the continuously increased thickness of AlOx 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 AlOx interlayer self-formed at the MoO3/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.