Amorphous silicon carbide high contrast gratings as highly efficient spectrally selective visible reflectors.

We report spectrally selective visible wavelength reflectors using hydrogenated amorphous silicon carbide (a-SiC:H) as a high index contrast material. Beyond 610nm and through the near infrared spectrum, a-SiC:H exhibits very low loss and exhibits an wavelength averaged index of refraction of n = 3.1. Here we design, fabricate, and characterize such visible reflectors using a hexagonal array of a-SiC:H nanopillars as wavelength-selective mirrors with a stop-band of approximately 40 nm full-width at half maximum. The fabricated high contrast grating exhibits reflectivity R >94% at a resonance wavelength of 642nm with a single layer of a-SiC:H nanopillars. The resonance wavelength is tunable by adjusting the geometrical parameters of the a-SiC:H nanopillar array, and we observe a stop-band spectral center shift from 635 nm up to 642 nm. High contrast gratings formed from a-SiC:H nanopillars are a promising platform for various visible wavelength nanophotonics applications.

Triple-halide wide-band gap perovskites with suppressed phase segregation for efficient tandems.

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 30% 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 1.67-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 100-sun illumination intensity and less than 4% degradation in semitransparent top cells after 1000 hours of maximum power point (MPP) operation at 60°C. By integrating these top cells with silicon bottom cells, we achieved a PCE of 27% in two-terminal monolithic tandems with an area of 1 square centimeter.