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.