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.

Silicon Heterojunction Microcells.

We report the design, fabrication, and characterization of silicon heterojunction microcells, a new type of photovoltaic cell that leverages high-efficiency bulk wafers in a microscale form factor, while also addressing the challenge of passivating microcell sidewalls to mitigate carrier recombination. We present synthesis methods exploiting either dry etching or laser cutting to realize microcells with native oxide-based edge passivation. Measured microcell performance for both fabrication processes is compared to that in simulations. We characterize the dependence of microcell open-circuit voltage (Voc) on the cell area-perimeter ratio and examine synthesis processes that affect edge passivation quality, such as sidewall damage removal, the passivation material, and the deposition technique. We report the highest Si microcell Voc to date (588 mV, for a 400 µm × 400 µm × 80 µm device), demonstrate Voc improvements with deposited edge passivation of up to 55 mV, and outline a pathway to achieve microcell efficiencies surpassing 15% for such device sizes.