High efficiency quantum well waveguide solar cells and methods for constructing the same

摘要

Photon absorption, and thus current generation, is hindered in conventional thin-film solar cell designs, including quantum well structures, by the limited path length of incident light passing vertically through the device. Optical scattering into lateral waveguide structures provides a physical mechanism to increase photocurrent generation through in-plane light trapping. However, the insertion of wells of high refractive index material with lower energy gap into the device structure often results in lower voltage operation, and hence lower photovoltaic power conversion efficiency. The voltage output of an InGaAs quantum well waveguide photovoltaic device can be increased by employing a III-V material structure with an extended wide band gap emitter heterojunction. Analysis of the light IV characteristics reveals that non-radiative recombination components of the underlying dark diode current have been reduced, exposing the limiting radiative recombination component and providing a pathway for realizing solar-electric conversion efficiency of 30% or more in single junction cells.

主权项

1. A photovoltaic device comprising:
a base layer, a step-graded quantum well comprising InGaAs, the step-graded quantum well embedded within the base layer, the step-graded quantum well forming a series of approximately 35 meV energy steps between each step; and an extended emitter region disposed directly adjacent to the base layer, thereby falling within a junction depletion region, the extended emitter including a lightly or undoped first material having a higher energy gap than the base layer; an emitter disposed adjacent to the extended emitter region, the emitter including a second material having a higher energy gap and opposite doping polarity than the base layer.