Indium Tin Oxide-Free Polymer Solar Cells: Microcavity Enhancing the Performance Using WO3/Au/WO3 as Transparent Electrode

Recently, indium tin oxide (ITO)-free polymer solar cells (PSCs) have attracted increasing attention due to expensive ITO price caused by rare and valuable element-indium. Here, we fabricated and investigated ITO-free PSCs with the structure of glass/WO
₃
/Au/WO
₃
/poly (3-hexylthiophene): indene-C
₆₀
bisadduct (P3HT:ICBA)/LiF/Al. It is demonstrated that the power conversion efficiency of ITO-free devices with 85-nm-thick active layer is improved by 21.2% compared with that of ITO-based. The improvement is attributed to the first-order resonance and near-resonance of microcavity effect constructed between the Au anode and top Al cathode. The judgment is supported by the incident photon-to-electron conversion efficiency spectra test and optical simulation based on transfer matrix method, which reveal that the microcavity structure can enhance light absorption within two discrete wavelength ranges of 390-460 and 510-660 nm.