Flexible inverted polymer solar cells with an indium-free tri-layer cathode

Indium tin oxide (ITO)-free inverted polymer solar cells (PSCs) have been fabricated without the need of an additional electron transport layer. The indium-free transparent electrode consists of a tri-layer stack ZnO (30 nm)/Ag (14 nm)/ZnO (30 nm) deposited on glass and plastic substrates via ion-beam sputtering. The tri-layer electrodes exhibit similar physical properties to its ITO counterpart, specifically yielding high transmittance and low resistivity (76.5% T at 550 nm, R_sq of 8 Ω□) on plastic substrates. The novel tri-layer electrode allows for the fabrication of inverted PSCs without the additional ZnO interfacial layer commonly deposited between ITO and the photoactive layer. This allows for the preparation of thinner plastic solar cells using less material than conventional architectures. Initial studies involving the newly realized architecture (tri-layer electrode/P3HT:PCBM/PEDOT: PSS/Ag) have shown great promise for the transition from ITO to other viable electrodes in organic electronics.