Solvent-Resistant Colorless Polyimide-Silver Nanowire Hybrid Films for Double-Sided Transparent Electrodes in Perovskite Solar Cells

Highly transparent colorless polyimide (CPI) films were synthesized via thermal imidization using 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diamine (TFMB) and 1,3,5-tris(4-aminophenyl)benzene (TAPB) monomers at ratios of 8:2 (s-CPI-8:2) and 9:1 (s-CPI-9:1). A reference film (i-CPI) was prepared by using only 6FDA and TFMB. FTIR and TGA confirmed the polymer structures and thermal stability. The transmittance of all three CPI films at 550 nm was above 99%, and the s-CPI films showed better solvent resistance compared with i-CPI. Specifically, i-CPI was completely dissolved in N,N-dimethylformamide and chloroform solvents after 24 h of immersion, whereas the residual masses of s-CPI-8:2 in N,N-dimethylformamide (DMF) and CHCl3 were 88.41 and 96.53% after 24 h of immersion. Flexible CPI AgNW composite electrodes, fabricated via an inverted layer-by-layer process, achieved a sheet resistance of 8.41 Ω/sq and 83.06% transmittance at 550 nm. The surface roughness of the electrode is reduced from 4.11 to 0.41 nm, and the square resistance remains stable after 5000 bending cycles, while the sheet resistance R/R0 is only 1.06 after 50 stripping cycles. s-CPI-8:2/AgNW/SnO2-based perovskite solar cells have a photovoltaic efficiency of 10.96% on the ITO side, which shows potential for bifacial applications.