Performance Improvement of Low-Band-Gap Polymer Solar Cells by Optical Microcavity Effect

We investigate the performance of the indium tin oxide (ITO)-free low-band-gap polymer solar cells (PSCs) with a WO
₃
/Ag/WO
₃
multilayer as a transparent electrode. For the device with a 60-nm-thick active layer, the efficiency is improved by 26.5% when compared with that of the device with an ITO electrode. The improvement can be attributed to the resonance effect of the microcavity structure occurring between the transparent WO
₃
/Ag/WO
₃
and top metal electrode. Further investigation based on the incident photon-to-electron conversion efficiency spectra test and transfer matrix simulation is performed to expatiate on the effects of the microcavity on the performance of the low-band-gap PSCs with the WO
₃
/Ag/WO
₃
multilayer as the transparent electrode.