High-Quality PEI/Ag/PEI-Zn Semitransparent Electrode for Efficient ITO-Free Flexible Organic Solar Cells and Perovskite Solar Cells

To achieve significant advancements in flexible organic and perovskite solar cells, it is imperative to develop a flexible semitransparent electrode that possesses higher light transmittance, lower square resistance, and a flexible bending quality. In this research, we propose a high-quality flexible polyethyleneimine (PEI)/Ag/PEI-Zn electrode on common polyethylene naphthalate (PEN), polyethylene terephthalate (PET), and Polydimethylsiloxane (PDMS) flexible substrates to enhance the transmittance of conventional Ag ultrathin film electrodes in the visible wavelength range. The power conversion efficiency (PCE) of flexible OSC devices based on Poly[(2,6-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene)-co-(1,3-di(5-thienyl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c']dithiophene-4,8-dione)] (PBDB-T-SF): IT-4F active layer achieves an optimal performance by annealing the PEI-Zn layer at 130 °C through chelating Zn ions with PEI. The PEI-Zn layer serves as a high-quality electron transporting property and surface modifying layer on Ag film. Also, the PEI/Ag/PEI-Zn electrode exhibited remarkable mechanical durability of flexible organic solar cells (FOSCs) compared with indium tin oxiden (ITO)-based devices in consecutive bending experiments. PEI/Ag/PEI-Zn electrode was also applied in flexible perovskite solar cells. Their PCE performance reaches as high as 19.24% and also maintains 73% of its initial value after 500 bending cycles, which is much better than ITO-based flexible devices. Above all, both enhancement in light transmittance and PCE performance of both FOSCs and FPSCs underscores the superior properties of PEI/Ag/PEI-Zn flexible electrodes.