Indium tin oxide-free transparent and conductive electrode based on SnOx |Ag| SnOx for organic solar cells

A SnOx vertical bar Ag vertical bar SnOx multilayer deposited by E-beam evaporation is proposed as transparent anode for a (poly-3-hexylthiophene):[6,6]-phenyl-C-61-butyric acid methyl ester (P3HT: PCBM) bulk heterojunction based Organic Solar Cell (OSC). Such multilayers are studied and manufactured with the objective to give to the electrode its best conductivity and transparency in the visible spectral range. A transfer matrix method numerical optimization of the thicknesses of each layer of the electrode is developed to limit the number of test samples which would have been manufactured whether an empirical method was chosen. Optical characterization of the deposited SnOx and Ag thin films is performed to determine the dispersion of the complex refractive indices which are used as input parameters in the model. A satisfying agreement between numerical and experimental optical properties is found. The bare tri-layer electrodes show low sheet resistance (as low as 6.7 Omega/square) and the whole Glass vertical bar SnOx vertical bar Ag vertical bar SnOx structure presents a mean transparency on 400-700 nm spectral band as high as 67%. The multilayer is then numerically studied as anode for a P3HT: PCBM bulk heterojunction based OSC. Intrinsic absorption inside the sole active layer is calculated giving the possibility to perform optical optimization on the intrinsic absorption efficiency inside the active area by considering the media embedding the electrodes. An additional study using the morphology of the silver inserted between both oxide layers as input data is performed with a finite difference time domain 3D-method to improve the accordance between optical measurements and numerical results. (C) 2014 AIP Publishing LLC.