Anti-Corrosion Layer Embedded Top Cathode for Semi-Transparent Perovskite Solar Cells

Abstract

Power conversion efficiency (PCE) of perovskite solar cells (PSCs) has exceeded 25%, which is comparable to that of silicon solar cells and makes PSCs promising candidates for the next generation photovoltaics. However, their commercialization is still seriously hindered by the low device stability. Besides the well-known thermal and chemical factors, another major cause of the instability is the interaction of top metal electrodes with the Iodine-containing compounds decomposed from perovskite absorber layers. Both these volatile compounds and metal atoms can diffuse towards each other through hole transport layers and consequently lead to the degradation of device performance. In order to resolve this problem, an anti-corrosion layer against undesired mass transport is required to be inserted between the metal electrode and the perovskite absorber layer. Molybdenum is intrinsically resistant to the corrosive reaction of Mo to MoI3 because of its higher Metal-Metal bonding energy (435.5 kJ/mol) than Metal-Iodine bonding energy (266.9 kJ/mol). Besides, it has also been proven that Mo is stable against metal atom diffusion into perovskite by theory analysis. In this work, Mo was chosen to act as the anti-corrosion layer embedded in Oxide/Metal/Oxide (OMO) transparent cathodes for inverted semi-transparent PSCs. Bottom indium zinc tin oxide (IZTO) layers with a thickness of 30nm were fabricated via facing target sputtering using a low power before the deposition of magnetron sputtered Mo to protect organic layers from sputter damage. The electrical and optical characteristics of IZTO/Mo/IZTO (IMI) transparent electrodes were analyzed with dependence on Mo thickness and top IZTO thickness. Inverted semi-transparent PSCs integrated with the optimized IMI top cathode were assembled, in which the diffusion of iodine ions and metal atoms were more efficiently blocked compared to the reference device without a Mo anti-corrosion layer.