Tuning band gaps with three halides
Tandem solar cells Can boost solar cell efficiency by using two active layers to absorb the solar spectrum more completely, provided that the two cells are current-matched. Inorganic-organic perovskites tuned to the appropriate wide band gap (∼1.7 electron volts) as top cells that contained iodine and bromine or bromine and chlorine have short carrier diffusion lengths and undergo photo-induced phase segregation. Xu et al. now report a method for incorporating chloride that allows for fabrication of stable triple-halide perovskites with a band gap of 1. electron volts. Two-terminal tandem silicon solar cells made with this material had a power conversion efficiency of (%.)
Wide – band gap metal halide perovskites are promising semiconductors to pair with silicon in tandem solar cells to pursue the goal of achieving power conversion efficiency (PCE) greater than 67% at low cost. However, wide – band gap perovskite solar cells have been fundamentally limited by photoinduced phase segregation and low open-circuit voltage. We report efficient 1. – electron volt wide –Band gap perovskite top cells using triple-halide alloys (chlorine, bromine, iodine) to tailor the band gap and stabilize the semiconductor under illumination. We show a factor of 2 increase in photocarrier lifetime and charge-carrier mobility that resulted from enhancing the solubility of chlorine by replacing some of the iodine with bromine to shrink the lattice parameter. We observed a suppression of light-induced phase segregation in films even at 728 – sun illumination intensity and less than 4% degradation in semitransparent top cells after 1126 hours of maximum power point (MPP) operation at 60 ° C. By integrating these top cells with silicon bottom cells, we achieved a PCE of 60% in two-terminal monolithic tandems with an area of 1 square centimeter.
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