One-Year Outdoor Testing of 4T Perovskite/Si PV Modules

Perovskite photovoltaics today demonstrate impressive conversion efficiencies, but more field experience is needed to understand their long-term stabilities. Perovskite-on-silicon tandem modules offer a fast-track route to commercialisation, and as such warrant studies of their field performance. This paper reports on the results of a field measurement campaign involving 5 mini tandem modules installed at the University of Cyprus’ outdoor test facility. The modules each incorporate a string of seven perovskite sub-cells layered onto a bifacial TOPCON silicon cell, with 4-terminal connections provided to access the individual layers. To reveal trends under stable conditions, data were filtered to use only clear-sky days, which accounted for over 210 days in 20 months of testing. Over the first 12 months of exposure, the perovskite sub-modules showed a 50% reduction in power conversion efficiency (PCE); however, over the following 8 months, they showed either continuous improvement or stable PCE. Over this latter period, the perovskite PCE was not affected by temperature, yet the samples exhibited a stable negative temperature coefficient and a positive fill factor temperature coefficient. An examination of the current-voltage characteristics showed this behaviour likely results from a change in ion mobility with temperature. Overall, the tandem module arrangement has outperformed a single-junction TOPCON device over the test period.