The effect of hole transfer layers and anodes on indium-free TiO₂/Ag/TiO₂ electrode and ITO electrode based P3HT:PCBM organic solar cells

Transparent composite electrodes (TCE), TiO₂/Ag/TiO₂ (TAgT), have been demonstrated as a promising alternative of indium tin oxide (ITO) in organic solar cell application. TiO₂/Ag/TiO₂ have been incorporated into bulk heterojunction organic solar cells (OSCs) to replace ITO as the anode. Two different hole transfer layers (HTL), poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) and MoO₃, are compared in terms of their compatibility with the TiO₂/Ag/TiO₂ anode. The MoO₃ layer has been shown to be a beneficial HTL for TiO₂/Ag/TiO₂ based OSC. However, the wettability of MoO₃ for polymer blend is not as good as PEDOT:PSS, and results in a relatively thin active layer in OSCs. On the other hand, ITO based OSCs using PEDOT:PSS and MoO₃ as the HTL are fabricated as control samples to compare the performance of TAgT and ITO anodes. Results of the investigation shows that the superior electrical property of TAgT anodes contributes to the effective collection of photo-carriers and its lower optical transmittance barely degrades the light absorption in OSCs. In a few words, the higher Haacke figure of merit of TAgT enables better performance of OSCs with MoO₃ HTL, in comparison with ITO based OSC.