Part I: High Efficiency CIS Solar Cells with Simple Fabrication Method

CIS has a very high optical absorption coefficient, which makes it able to absorb more than 90% of the incident photons with energies higher than 1.04 eV within 1-2 µm thickness. Because of the high absorption coefficient and low bandgap, high quality CIS solar cells can have a very high short circuit current compared with other thin film material or other type of solar cells. We offer a very simple two-step process based on annealing stacked elemental layers under selenium vapor within a graphite box, followed by a potassium fluoride postdeposition treatment, which is a low-cost and highly manufacturable approach. We are able to reproducibly achieve above 12% conversion efficiency, with the champion cell exhibiting near-record 14.7% efficiency. Our results indicate that perhaps the CIS system is less sensitive to elaborate processing steps and details than previously thought. This simple approach offers a very useful experimental platform from which to study a variety of thin film PV research topics, including the possibility of producing tandem solar cell by also using perovskite.

Part II: Waveguides Bragg Gratings in Integrated Photonics

Integrated photonics on silicon-based material combines two great inventions of the last century: silicon technology and photonic technology. It is paving the way for a monolithically integrated optoelectronic platform on a single chip. Being a prevailing research topic in the past decade, it has seen tremendous progress with the successful development of high-performance components. Among all integrated photonics platforms, the silicon nitride planar waveguide platform provides benefits like low optical losses, transparency over a wide wavelength range (400-2350 nm), compatibility with CMOS and wafer-scale foundry processes, and high-power handling capabilities.

In this part, waveguides Bragg gratings are investigated to improve the performance of several integrated photonics components. An 83-dB rejection ratio pump filter using a periodic waveguide Bragg grating with an efficient z-shape waveguide design to suppress the TM mode and avoid scattered modes is demonstrated. Fabry-Perot cavity enhanced four-wave mixing devices are optimized based on a numerical model developed with an ABCD matrix method and four-wave mixing in a Fabry-Perot cavity that uses grating is demonstrated experimentally. Finally, to reduce the pixel size and power consumption of optical phased array for virtual reality applications, complex waveguide Bragg gratings are generated via both Layer Peeling/Adding algorithm and genetic algorithm to support slow-light modes over certain bandwidth.