Multi-junction silicon solar cells are an energy efficient addition to the photovoltaics toolbox but their high cost can prove prohibitive to wide technology diffusion. An opportunity for improving the economic attractiveness of Perovskite/silicon tandem solar cells offer potential to deliver module efficiency gains at minimal cost. Source: Dennis Schroeder/NRELthese tandem devices while also boosting solar conversion efficiency has been explored.

Researchers from the University of Colorado Boulder, National Renewable Energy Laboratory (NREL), Stanford University and Arizona State University paired wide band gap metal halide perovskites with silicon. Chlorine, bromine and iodine were applied to the less expensive perovskite layer to tailor the bandgap and stabilize the semiconductor under illumination.

Inclusion of chlorine allowed for fabrication of stable triple-halide perovskites with a band gap of 1.67 electron volts. Two-terminal tandem silicon solar cells synthesized with this material had a power conversion efficiency of 27%, considerably higher than the 21% achieved by a silicon cell without the perovskite layer.

The new 1 cm² solar cells showed less than 4% degradation in semitransparent top cells after 1,000 hours of maximum power point operation at 60° C.