Large-Area (Ag,Cu)(In,Ga)Se2 Thin-Film Solar Cells with Increased Bandgap and Reduced Voltage Losses Realized with Bulk Defect Reduction and Front-Grading of the Absorber Bandgap

Alexandra Bothwell, Siming Li, Rouin Farshchi, Michael Miller, Jake Wands, Craig Perkins, Angus Rockett, Aaron Arehart, Darius Kuciauskas

Research output: Contribution to journalArticlepeer-review

7 Scopus Citations

Abstract

The 1.24 eV bandgap, 18.8% power conversion efficiency Ag-alloyed chalcopyrite (Ag,Cu)(In,Ga)Se2 (ACIGS) solar cells are characterized to relate voltage and efficiency improvements to electro-optical (EO) characteristics. Shockley–Read–Hall recombination center defect density, identified and characterized through deep level transient spectroscopy and time-resolved photoluminescence (TRPL), is reduced through potassium and copper treatment optimization. Concomitantly, longer minority carrier lifetimes are achieved, which increases open-circuit voltage (VOC). Near-conduction band defects associated in earlier studies with light-induced current instability are also mitigated. Analysis of charge-carrier dynamics after single- and two-photon excitation is used to separate recombination at the front interface and in the absorber bulk. From TRPL decay simulations, the authors estimate ranges of key solar cell material characteristics: bulk carrier lifetime τbulk = 110–210 ns, charge-carrier mobility μ = 110–160 cm2V−1s−1, and front interface recombination velocity Sfront = 700–1050 cm s−1. This lowest-reported Sfront for ACIGS absorbers originates from the notched conduction band grading, which also makes the impact of the back interface recombination negligible. It is suggested in the results that solar cell performance enhancements can be made most readily with two distinct strategies: improving device architecture and reducing semiconductor defect densities. Using these approaches, power conversion efficiency in large-area solar cells is improved by 1.1% absolute.

Original languageAmerican English
Article number2200230
Number of pages13
JournalSolar RRL
Volume6
Issue number8
DOIs
StatePublished - 2022

Bibliographical note

Publisher Copyright:
© 2022 The Authors. Solar RRL published by Wiley-VCH GmbH.

NREL Publication Number

  • NREL/JA-5900-82727

Keywords

  • absorber grading
  • ACIGS
  • defects
  • solar cells
  • voltage losses

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