Photon and carrier management design for nonplanar thin-film copper indium gallium selenide photovoltaics

Abstract

Nonplanar structured photovoltaic absorber design has potential to achieve high solar cell efficiency with significantly reduced material use. We report optoelectronic simulations that highlight photon and generated carrier management opportunities for improvement of thin film Cu(In_xGa_(1−x))Se_2 (CIGS) device performance. Structures realized via either self-assembly or patterning via nanoimprint lithography, and also a combination of both are predicted to exhibit significant increases in short circuit current density and open circuit voltage simultaneously. The structures investigated include: 1) self-assembled nonplanar structures that strongly scatter incident light and enhance carrier generation near regions of high electric potential, 2) lithographically-patterned embedded periodic dielectric structures, 3) planar dielectric layers that separate the CIGS absorber from the molybdenum back-contact via reduced-area contacts that minimize optical and electronic losses, 4) a combination of these for combined effects. We find that the self-assembled nonplanar CIGS cells with 700 nm planar equivalent thickness, combined with dielectric separation layers yield increases in short circuit current density and open circuit voltage up to 3.4 mA cm−2 and 29 mV, respectively. The absolute efficiency increases from 15.4% to 18.1%, compared to the predicted efficiency for planar CIGS thin film cells of equivalent thickness. The addition of a single layer MgF_2 anti-reflection coating brings the maximum predicted efficiency up to 19.7% for randomly textured devices.

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