The optimal TiO2/Ag/TiO2 electrode for organic solar cell application with high device-specific Haacke figure of merit

Abstract

As a promising indium-free electrode, transparent composite electrode (TCE) TiO2/Ag/TiO2 is an attractive alternative to indium tin oxide (ITO). The multilayer structure of TiO2/Ag/TiO2 is deposited on glass substrate by room-temperature sputtering. The effects of deposition rate, thickness of Ag and TiO2 layers on the electrical and optical properties of this TCE are presented. Results show that the Ag films tend to have fewer voids to form, if the Ag deposition rate is sufficiently high. The presence of fewer voids in the Ag layer results in higher transmittance and lower sheet resistance of the corresponding TiO2/Ag/TiO2 structure. In order to increase the solar input to the P3HT:PC61BM organic solar cell, the layer thicknesses of TiO2/Ag/TiO2 electrodes are theoretically and then experimentally optimized, such that its optical transmittances are maximized across the wavelength range where the light absorption of P3HT:PC61BM is highest. In this study, the device-specific Haacke figure of merit (FOM) of the TiO2/Ag/TiO2 electrode is optimal with the use of 42nm TiO2 layers and 10nm Ag layer. This optimal Haacke FOM is two times higher than that of ITO electrodes. The conventional bulk heterojunction organic solar cell (OSC) fabricated on optimized TiO2/Ag/TiO2 electrode shows high power conversion efficiency (PCE), almost 100% higher than PCE of OSC fabricated on ITO. Our finding indicates that TiO2/Ag/TiO2 electrode can be specifically tailored to particular applications. It can be implemented in organic solar cell and has considerable potential to replace ITO in solar cell applications.