Semitransparent Organic Solar Cells Enabled by Facile-Synthesis Cyano-Functionalized Polyfluorenes as a Third Component

Semitransparent organic solar cells (ST-OSCs) require carefully selected active layer materials to achieve an optimal balance between photoelectric conversion efficiency (PCE) and average visible transmittance (AVT). Here, we present a facile processable polyfluorene, PFFCN, blended with a medium-bandgap polymer donor (PM6) and a narrow-bandgap nonfullerene acceptor (Y6) to form a ternary active layer. By adjustment of the ratio of PFFCN, the AVT of the active layer can be enhanced without altering the active layer thickness. With the blend PFFCN/PM6/Y6 = 0.3:1.0:1.5, the AVT of the active layer can reach 31% at 100 nm thickness compared to an AVT of 22% for the binary PM6/Y6 (1.3:1.5) active layer. Further increasing the PFFCN content (0.65:0.65:1.5) results in an AVT of 42%, demonstrating its effectiveness in improving light transparency. Following a silver (Ag) top electrode deposition, the ternary ST-OSC with 0.3 PFFCN incorporation maintains a PCE of 12.23%, comparable to 13.45% of the binary PM6/Y6 device. However, at higher PFFCN ratios (0.65:0.65:1.5), a significant decline in PCE is observed, suggesting reduced phase compatibility among the components.