Coloring Semitransparent Perovskite Solar Cells via Dielectric Mirrors.

While perovskite-based semitransparent solar cells for window applications show competitive levels of transparency and efficiency compared to organic photovoltaics, the color perception of the perovskite films is highly restricted since bandgap engineering would result in losses in power conversion efficiencies. To overcome the limitation in visual aesthetics, we combined semitransparent perovskite solar cells with dielectric mirrors. This approach enables to tailor the device appearance to almost any desired color and simultaneously offers additional light harvesting for the solar cell. In the present work, opto-electrical effects are investigated through quantum efficiency and UV-to-visible spectroscopic measurements. Likewise, a detailed chromaticity analysis, featuring the transmissive and reflective color perception of the device including the mirror, from both sides and in different illumination conditions, is presented and analyzed. Photocurrent density enhancement of up to 21% along with overall device transparency values of up to 31% (4.2% efficiency) are demonstrated for cells showing a colored aesthetic appeal. Finally, a series of simulations emulating the device chromaticity, transparency and increased photocurrent density as a function of the photoactive layer thickness and the design wavelength of the dielectric mirror is presented. Our simulations and their experimental validation enabled us to establish the design rules that consider the color-efficiency-transparency interplay for real applications.