Improved Performance of Polymer Solar Cells by Thermal Evaporation of AgAl Alloy Nanostructures into the Hole-Transport Layer

The performance characteristics of polymer solar cells (PSCs) incorporated with AgAl and Ag nanostructures and MoO₃ spacer layers were investigated. The power conversion efficiency (PCE) of PSCs is sensitive to the nominal thicknesses of the AgAl nanostructures and the MoO₃ spacer layer. The PCE of a PSC with a 3-nm-thick layer of AgAl nanostructures and a 1-nm-thick MoO₃ isolation layer reached 9.79%, which is higher than the PCE (8.55%) of the reference PSC without metal nanostructures. Compared to PSCs with Ag nanostructures, PSCs with AgAl nanostructures showed better stability and still retained 60% of their initial PCE values after aging for 120 days in air without encapsulation. The enhanced stability of the PSCs is attributed to the formation of AlO_x, which can inhibit the diffusion of Ag atoms into the neighboring layer. The localized surface plasmonic resonance (LSPR) effect of AgAl nanostructures was retained by inserting an only 1-nm-thick MoO₃ spacer layer between the metal nanostructures and the metal electrode. Our work has demonstrated that using AgAl alloy instead of Ag as plasmonic nanostructures is a better strategy for improving the performance of PSCs, especially in terms of the stability of the cells.