With the unprecedented efficiency upraise of perovskite-based photovoltaics, the interest in its semitransparent configuration has gained momentum during the last two years. The attention on the optimization of mono-facial and bi-facial architectures is further fostered by the requirements for building integrated photovoltaic applications as well as for tandem photovoltaic. Despite encouraging predictions, the later faces critical challenges mainly due to unwanted parasitic absorption and light reflection losses. These losses are identified to be emanating mainly from absorption in the electrode and from the reflection at the first selective-contact/perovskite interface.
In this work, we present an approach for elucidating the opto-electrical effects of nano structured transparent electrodes on bifacial device performance. As opposed to previous reports were the improvement of efficiency is done through energy-intensive deposition of both top and bottom electrodes, here we demonstrate that solution processed silver nanowires, a prototype composite for percolation-based electrodes, allows minimizing the overall optical and electrical losses with outstanding precision by a simple spray coating process. Particularly, we show with a combination of optical and photo-physical studies that when illuminated from the top electrode, the spectrally resolved photocurrent generation losses are mostly dominated by parasitic light absorption rather than being limited by the optical and bulk conductivity.
This optical attenuation then governs the spectral response for sheet resistances in a lower regime. An optimum trade-off must be identified. We further minimized the parasitic absorption and Fresnel reflection of the device architecture by the selection and optimization of wide-band gap semiconductors as selective contacts. As a result we present a solution-processed perovskite-based solar cell with 19.4% efficiency, which translated into a semitransparent solar cell with 16.9% efficiency. Our devices present an enhanced overall optical transmission particularly extended to the near infrared allowing the elaboration of 4- terminal silicon/perovskite tandem devices with 23.7% efficiency. The initial silicon cell was then improved in efficiency by 26.7%.