Design and Demonstration of High-Efficiency Quantum Well Solar Cells Employing Thin Strained Superlattices

Roger E Welser,Anastasiia Fedorenko,Mitsul Kacharia,Ashok K Sood,Seth M Hubbard,Stephen J Polly

doi:10.1038/s41598-019-50321-x

Roger E Welser, Anastasiia Fedorenko + Show 4 more

Open Access

https://doi.org/10.1038/s41598-019-50321-x

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Abstract

Nanostructured quantum well and quantum dot III–V solar cells provide a pathway to implement advanced single-junction photovoltaic device designs that can capture energy typically lost in traditional solar cells. To realize such high-efficiency single-junction devices, nanostructured device designs must be developed that maximize the open circuit voltage by minimizing both non-radiative and radiative components of the diode dark current. In this work, a study of the impact of barrier thickness in strained multiple quantum well solar cell structures suggests that apparent radiative efficiency is suppressed, and the collection efficiency is enhanced, at a quantum well barrier thickness of 4 nm or less. The observed changes in measured infrared external quantum efficiency and relative luminescence intensity in these thin barrier structures is attributed to increased wavefunction coupling and enhanced carrier transport across the quantum well region typically associated with the formation of a superlattice under a built-in field. In describing these effects, a high efficiency (>26% AM1.5) single-junction quantum well solar cell is demonstrated in a device structure employing both a strained superlattice and a heterojunction emitter.

Highlights

The short circuit current density (JSC), by employing strain-compensation techniques to add as many layers as possible to the QW absorber region[18]
Nanostructured quantum well and quantum dot solar cells have been widely investigated as a means of extending infrared absorption and enhancing III–V photovoltaic device performance
A single-junction nanostructured III–V solar cell with 1-sun efficiency exceeding 26% has been demonstrated under AM1.5 illumination

Summary

Introduction

The short circuit current density (JSC), by employing strain-compensation techniques to add as many layers as possible to the QW absorber region[18]. The impact of inter-QW GaAs barrier thickness on solar cell absorption and emissions is systematically investigated in both N-on-P GaAs homojunction and P-on-N In0.49Ga0.51P/ GaAs heterojunction device structures incorporating strained, defect-free In0.08Ga0.92As (hereafter, ‘InGaAs’) QWs. Measurements of the spectral response (SR) and luminescence characteristics of these devices indicate that reducing the GaAs barrier thickness both enhances carrier collection from the QWs and reduces radiative recombination within the strained InGaAs well region. Measurements of the spectral response (SR) and luminescence characteristics of these devices indicate that reducing the GaAs barrier thickness both enhances carrier collection from the QWs and reduces radiative recombination within the strained InGaAs well region This observation is consistent with increased carrier delocalization and separation as the barrier thickness decreases and superlattice effects dominate (e.g. miniband formation, Wannier-Stark hopping, and/or sequential tunneling)[23,24,25,26]. After adding a two-layer antireflection coating, an encouragingly high one-sun efficiency of greater than 26% in a single-junction quantum well solar cell was obtained under standard AM1.5 illumination

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