The front contact has a major impact on the electrical and optical properties of perovskite solar cells. The front contact is part of the junction of the solar cell and must provide lateral charge transport to the terminals and should allow for an efficient light incoupling, while having low optical losses. The complex requirements of the perovskite solar front contact will be described and the optics of the front contact will be investigated. It will be shown that the front contact has a distinct influence on the short-circuit current and energy conversion efficiency. Metal oxide films were investigated as potential front contacts. The incoupling of light in the solar cell is investigated by three-dimensional finite-difference time-domain optical simulations and optical measurements of experimentally realized self-textured zinc oxide films. The zinc oxide films were prepared by metal-organic chemical vapor deposition at low temperatures. Furthermore, the influence of free carrier absorption of metal oxide films on the optics of low bandgap and/or tandem solar cells is investigated. Guidelines are provided on how to choose the doping concentration and thickness of the metal oxide films. Finally, it will be shown that by selecting an optimal front contact design the short-circuit current and energy conversion efficiency can be increased by at least 15%.
Keywords: TCO; light incoupling; light trapping; metal oxides; perovskite; solar cells; zinc oxide.