Calculation of the optical losses in perovskite solar cells

Perovskite solar cells (PSC) have been in development for a few years only, and quickly they have achieved high record efficiencies, above 23%, attracting great attention as a possible alternative to commercial Si solar cells. However, very few articles have dealt with the optical losses in this type of solar cells, but an important factor to be taken in account for developing highly efficient extra-thin solar cells, such as Perovskite Solar Cells, is the optical reflectance in the solar spectrum wavelength range for these devices. Reducing optical losses should cause improved photocurrent density and efficiency of the cell. Therefore, estimating the reflectance for each wavelength of the solar spectrum and the total average reflectance should help better design this kind of devices. Then, in this work we do calculations for planar multilayer perovskite solar cells using the Optical Matrix method for determining the expected reflectance as a function of wavelength, using refraction index and extinction coefficients for each of the materials that constitute the solar cells. Our results show that for very thin perovskite absorbers (less than 350 nm), the optical losses can become very high. Even for a typical perovskite thickness above 400 nm, the total average reflectance in the solar spectrum wavelength range can be as high as 10%, approximately. Then, in the future, a further increase of efficiency might be achieved by appropriate roughening of the perovskite layer surfaces.