SBIR-STTR Award

This proposal addresses the development of multi-junction solar cells for more complete utilization of the full solar spectrum. The approach uses a cell architecture based on an electrode nano-element array and a counter electrode array to achieve optimized light and carrier collection management (LCCM) inside a multi-junction device. The LCCM architecture applied to multi-junctions gives (1) enhanced absorption in all layers, (2) enhanced long wavelength absorption, (3) the freedom to reduce absorber layer thicknesses, due to the enhanced absorption, (4) the opportunity to use absorbers with lower carrier mobilities and lifetimes (i.e., thin film material utilization), and (5) reduced sensitivity to the light impingement angle. A six month effort for exploring this concept is proposed by a Solarity/University of Arkansas team which will have the tasks of (1) collecting data for candidate chalcogenide and III-V materials including band gap parameters (electron affinity and band gap) and optical properties (complex index of refraction), (2) assessment of possible multi-junction fabrication paths, (3) computer simulation of LCCM multi-junction performance, and computer device design optimization, and (4) technical determination of the overall feasibility of the LCCM approach to significantly improving full spectrum multi-junction performance.

Benefit:
Conventionally designed solar cells convert light into electricity by collecting photogenerated current carriers at their top and bottom electrode surfaces. This creates an undesirable trade-off between light absorption and charge collection, due to the limited thickness over which current can be efficiently harvested from the light absorbing material. Depositing the light absorbing material onto nanostructured electrodes circumvents this thickness limitation and offers additional light management benefits. The geometry (size and spacing) of the nanostructures can be customized to match the absorption and transport properties of the active layer material. These same parameters can be tuned to maximize light absorption, via photonic and plasmonic effects, even in thin devices. Solarity uses both computer modeling and experiment to optimize its nanostructured devices. The results of this research project are optimized designs for multijunction solar cells. The designs will offer devices well-suited for a variety of demanding applications including: military, commercial, and residential electricity generation.

Keywords:
light management, light management, CdSe, nanotechnology, Multijunction Solar Cells, Photovoltaic, InGa, InGaAs, CIGS