A Method for Efficient Transmittance Spectrum Prediction of Transparent Composite Electrodes

The interest in indium-free transparent composite electrode (TCE), a thin metal layer embedded between two transparent metal oxide (TMO) layers resulting in TMO/metal/TMO composite structure, has grown recently with the advent of their high figures of merit and its potential application in photovoltaic applications. However, most of the work to date has focused on experimentally producing the best optically transmitting TCE. To better design TCEs and minimize experimental work, it would be useful to develop a model that predicts the optical transmission. In the current work, the transfer-matrix method is employed to calculate the transmittance spectrum of TCE. To validate this approach, the transmittance spectra of TiO₂/Au/TiO₂ and TiO₂/Ag/TiO₂ multilayer thin-film TCEs are calculated with use of extracted material parameters. The calculated transmittance spectrum of TiO₂/Au/TiO₂ matches the measured spectrum quite well. However, the calcualted transmittance of TiO₂/Ag/TiO₂ is higher than its measured transmittance. The presence of voids in the Ag film is probably responsible for the decreased transmittance of the TiO₂/Ag/TiO₂ sample, and the continuous Au film in TiO₂/Au/TiO₂ ensures a good agreement between transmittance prediction and measurement. Our approach is a reliable tool to predict the optical transmittance of TCE with continuous films, and it can efficiently expedite the selection from numerous possible combinations of transparent metal oxides and metals when developing TCEs for future photovoltaic applications. It can also serve as a convenient method to assess the continuity of embedded metal layer.