Ultra-Thin Highly Absorbing Medium-Based Optical Nanocavity for Photonic and Optoelectronic Devices.

Abstract

Optical cavities, which generally consist of an optically transparent medium with wavelength-scale thickness, have been widely used in various areas ranging from lasers and modulators to sensors and filters. A trivial optical absorption in the cavity allows incident light to constructively interfere with reflected light many times without serious loss, thus being able to create a resonance at a certain wavelength. However, a traditional optical cavity has faced challenges in achieving an angle-insensitive property, thereby dramatically limiting their applications in a wide variety of fields. In this dissertation, we present several demonstrations, all based on optical nanocavities featuring strong resonance behaviors in highly absorbing media with the ultra-thin cavity thickness (< 30 nm) as compared to the wavelength of incident light, which is distinctly different from the conventional optical cavity systems. We firstly demonstrate angle invariant (up to 70°) transmissive and reflective structural color filters with high-color-purity exploiting a concept described above. We also present a new photovoltaic (PV) scheme incorporating novel optical design (ultra-thin cavity) and electrical design (dopant-free amorphous silicon) to create colored semitransparent PV cells, which could be harmoniously integrated with interiors and exteriors of the buildings, such as facades, windows, ceilings, and walls. This enables large surfaces of architectures to be efficiently utilized to generate the electric power. ~3 (2)% of power conversion efficiency with desired reflective (transmissive) colors that are insensitive to the angle of incidence and the polarization state of incident light is achieved. To improve the power conversion efficiency of the colored PV cells, we propose and experimentally demonstrate a spectrum splitting method and microcavity-integrated PV scheme, both of which show ~4% of power conversion efficiency. Lastly, we describe how our strategy could be applied to other applications, such as perovskite PV cells, broadband visible absorbers, and low reflective wire grid polarizers. The presented approach could open door to numerous applications, such as energy-efficient ultra-thin colored display technologies and decorative building-integrated PV.