Optimization of the perovskite cell in a bifacial two-terminal perovskite/silicon tandem module

Abstract

Bifacial perovskite/silicon solar cells can combine the advantages of tandem technology (high efficiencies) and bifacial modules (additional received irradiance from the rear) to increase the energy yield of photovoltaic (PV) systems further. In literature, it has already been shown that for two-terminal tandems this would require a lower bandgap energy ($E_g$) for the perovskite cell, as the rear irradiance increases the current in the bottom cell creating a current mismatch, if this is not considered during optimization. This work expands on bifacial two-terminal tandem optimization by considering aspects not included before. Besides the $E_g$, the thickness ($d$) of the perovskite is also optimized, as this also affects the current matching. Additionally, this work studies the trends in different energy losses of the PV module to better understand what affects the optimal perovskite cell. Our simulations show that the optimal $E_g$ is 1.61–1.65 eV and the optimal $d$ is 650–750 nm, which agrees with the observations in literature. The optimal $E_g$ and $d$ are mostly a trade-off between mismatch and thermalization losses, meaning that the mismatch losses should not be fully minimized. Additionally, the irradiance from the rear side is converted less efficiently than the front side irradiance due to larger thermalization and reflection losses. Therefore, the energy yield of bifacial tandem modules, compared to monofacial tandem ones, only increases for large ground albedo. Finally, our results show that the bifacial tandems have over a 25% gain in energy yield compared to bifacial single junction modules and up to 5% gain compared to monofacial tandem modules.