Quantum Dot-Based Thin-Film III–V Solar Cells

Abstract

In this work, we report our recent results in the development of thin-film III--V solar cells fabricated by epitaxial lift-off (ELO) combining quantum dots (QD) and light management structures. Possible paths to overcome two of the most relevant issues posed by quantum dot solar cells (QDSC), namely, the degradation of open circuit voltage and the weak photon harvesting by QDs, are evaluated both theoretically and experimentally. High open circuit voltage QDSCs grown by molecular beam epitaxy are demonstrated, both in wafer-based and ELO thin-film configuration. This paves the way to the implementation in the genuine thin-film structure of advanced photon management approaches to enhance the QD photocurrent and to further optimize the photovoltage. We show that the use of light trapping is essential to attain high-efficiency QDSCs. Based on transport and rigorous electromagnetic simulations, we derive design guidelines towards light-trapping enhanced thin-film QDSCs with efficiency higher than 28% under unconcentrated light, ambient temperature. If photon recycling can be fully exploited, 30% efficiency is deemed to be feasible. Towards this goal, results on the development and integration of optimized planar and micro-patterned mirrors, diffractive gratings and broadband antireflection coatings are presented.