Highly flexible transparent electrodes containing ultrathin silver for efficient polymer solar cells

Abstract

Transparent electrodes (TEs) having electrooptical trade-offs better than state-of-the-art indium tin oxide (ITO) are continuously sought as they are essential to enable flexible electronic and optoelectronic devices. In this work, a TiO2-Ag-ITO (TAI)-based TE is introduced and its use is demonstrated in an inverted polymer solar cell (I-PSCs). Thanks to the favorable nucleation and wetting conditions provided by the TiO2, the ultrathin silver film percolates and becomes continuous with high smoothness at very low thicknesses (3-4 nm), much lower than those required when it is directly deposited on a plastic or glass substrate. Compared to conventional ITO-TE, the proposed TAI-TE exhibits exceptionally lower electrical sheet resistance (6.2 sq(-1)), higher optical transmittance, a figure-of-merit two times larger, and mechanical flexibility, the latter confirmed by the fact that the resistance increases only 6.6% after 10(3) tensile bending cycles. The I-PSCs incorporating the TAI-TE show record power conversion efficiency (8.34%), maintained at 96% even after 400 bending cycles.