Understanding ERE and iVOC Metrics for Graded CdSeTe Absorbers

Journal Article · Thu Jun 26 00:00:00 UTC 2025 · Progress in Photovoltaics

DOI: https://doi.org/10.1002/pip.3922 · OSTI ID:2574725

Krasikov, Dmitry ^[1]; Kuciauskas, Darius  ^[2]; Scajev, Patrik ^[3]; Farshchi, Rouin ^[1]; McReynolds, Kevin ^[1]; Sankin, Igor ^[1]

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1. First Solar
2. National Renewable Energy Lab., Golden, CO (United States)
3. Vilnius University

PL-based external radiative efficiency (ERE) and implied open-circuit voltage (iVOC) metrics were introduced for thin-film solar absorbers to better understand the voltage deficit and diagnose losses in solar cells. Traditionally, elevated ERE and iVOC measurements are associated with diminished recombination within the solar device, a rationale heavily reliant on the assumption of a uniform bandgap and high carrier mobilities in the absorber. Recently, very low mobilities in CdSeTe absorbers (< 1 cm2/(V.s)) were measured using the light-induced transient grading technique. In this study, we use a detailed numerical model of iVOC to investigate the possible reasons of elevated iVOC in realistic CdSeTe absorbers with a graded Se profile. In particular, we examine how the bandgap nonuniformity and the reduced hole mobility in graded CdSeTe absorbers affect iVOC measurements. We show that high iVOC may result from inflated quasi-Fermi level splitting in the high-Se region in the front part of a CdSeTe absorber with slow hole transport. We reproduce the experimentally reported 360 mV increase in iVOC-VOC gap with reduced doping using a model with sub-1 cm2/(V.s) hole mobility in the high-Se region. Based on our results, we conclude that the iVOC metric (or ERE metric) should not be used as a sole metric of CdSeTe absorber quality. We discuss possible ways to extract useful information from the iVOC-VOC gap by supplementing the front-side illumination measurements with back-side illumination measurements.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office
• Grant/Contract Number: AC36-08GO28308
• OSTI ID: 2574725
• Report Number(s): NREL/JA-5900-91312
• Journal Information: Progress in Photovoltaics, Journal Name: Progress in Photovoltaics Journal Issue: 10 Vol. 33
• Country of Publication: United States
• Language: English