2, University of New South Wales, Sydney, New South Wales, Australia
3, University of Twente, Twente, , Netherlands
Perovskite solar cells are of great interest due to their potential for low cost and high performance. One of the challenges to attaining high photovoltaic conversion efficiency, particularly for large-area cells, is the tradeoff between the optical and electrical performance of the top contact. Because perovskite absorbers and selective electrode materials provide very little lateral conductivity for current collection, a transparent conductive oxide (TCO) such as indium tin oxide (ITO) must be used for the front contact. However, TCOs offer a tradeoff between transparency and conductivity, resulting in cells that slightly compromise both their short-circuit current density due to optical losses, and their fill factor due to resistive losses. A solution is to increase the density of the grid fingers such that thinner TCOs can be used; however, this increases the shading losses.
Recently, a method to produce effectively transparent front contact grids has been described (Adv. Optical Mater. 4 (10), 1470-1474 (2016); Photovoltaic Specialists Conference (PVSC) IEEE 43rd, 3612-3615, (2016); Sustainable Energy and Fuels, 1 (3), 593-598, (2017)). This approach yields a relatively dense array of high-aspect-ratio, triangular-shaped front contact fingers, in which light striking the metal is reflected towards the cell. We previously described the application of this technique to produce effectively transparent superstrates for perovskite solar cells, which based on optical absorption measurements, is expected to increase the short-circuit current density of perovskite solar cells by ~1 mA/cm2 (R. Saive, et al., PVSC 2018).
In the present work, we describe our efforts to integrate the effectively transparent superstrates with functional perovskite solar cells to realize the benefits of effectively transparent contacts (ETCs). We have investigated various combinations of perovskite absorbers and selective contact materials, and will report the results of our fabrication efforts. We are also investigating other approaches to integrate ETC technology with perovskite solar cells, including directly printing or transferring ETCs onto substrate-based perovskite cells topped with optimally thinned ITO layers.