Nanoscale Back Contact Perovskite Solar Cell Design for Improved Tandem Efficiency
Nano Letters, 17 (9):
5206-5212 (2017)PMID: 28782965.DOI: 10.1021/acs.nanolett.7b01092
Abstract
Tandem photovoltaics, combining absorber layers with two distinct band gap energies into a single device, provide a practical solution to reduce thermalization losses in solar energy conversion. Traditionally, tandem devices have been assembled using two-terminal (2-T) or four-terminal (4-T) configurations; the 2-T limits the tandem performance due to the series connection requiring current matching, while the standard 4-T configuration requires at least three transparent electrical contacts, which reduce the total collected power due to unavoidable parasitic absorption. Here, we introduce a novel architecture based on a nanoscale back-contact for a thin-film top cell in a three terminal (3-T) configuration. Using coupled optical–electrical modeling, we optimize this architecture for a planar perovskite-silicon tandem, highlighting the roles of nanoscale contacts to reduce the required perovskite electronic quality. For example, with an 18\% planar silicon base cell, the 3-T back contact design can reach a 32.9\% tandem efficiency with a 10 μm diffusion length perovskite material. Using the same perovskite quality, the 4-T and 2-T configurations only reach 30.2\% and 24.8\%, respectively. We also confirm that the same 3-T efficiency advantage applies when using 25\% efficient textured silicon base cells, where the tandems reach 35.2\% and 32.8\% efficiency for the 3-T, and 4-T configurations, respectively. Furthermore, because our design is based on the individual subcells being back-contacted, further improvements can be readily made by optimizing the front surface, which is left free for additional antireflective coating, light trapping, surface passivation, and photoluminescence outcoupling enhancements.