Radiative Efficiency Limit with Band Tailing Exceeds 30% for Quantum Dot Solar Cells
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acsenergylett.7b00923.pdf
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Author(s)
Holovský, Jakub
Jean, Joel
Mahony, Thomas Stephen
Bozyigit, Jonas Denis
Sponseller, Melany Christine
Bawendi, Moungi G
Bulovic, Vladimir
Date Issued
October 2017
Journal
ACS Energy Letters
Publisher
American Chemical Society (ACS)
Citation
Jean, Joel et al. “Radiative Efficiency Limit with Band Tailing Exceeds 30% for Quantum Dot Solar Cells.” ACS Energy Letters 2, 11 (October 2017): 2616–2624 © 2017 American Chemical Society
Version
Final published version
Abstract
Thin films of colloidal quantum dots (QDs) are promising solar photovoltaic (PV) absorbers in spite of their disordered nature. Disordered PV materials face a power conversion efficiency limit lower than the ideal Shockley-Queisser bound because of increased radiative recombination through band-tail states. However, investigations of band tailing in QD solar cells have been largely restricted to indirect measurements, leaving their ultimate efficiency in question. Here we use photothermal deflection spectroscopy (PDS) to robustly characterize the absorption edge of lead sulfide (PbS) QD films for different bandgaps, ligands, and processing conditions used in leading devices. We also present a comprehensive overview of band tailing in many commercial and emerging PV technologies - including c-Si, GaAs, a-Si:H, CdTe, CIGS, and perovskites - then calculate detailed-balance efficiency limits incorporating Urbach band tailing for each technology. Our PDS measurements on PbS QDs show sharp exponential band tails, with Urbach energies of 22 ± 1 meV for iodide-treated films and 24 ± 1 meV for ethanedithiol-treated films, comparable to those of polycrystalline CdTe and CIGS films. From these results, we calculate a maximum efficiency of 31%, close to the ideal limit without band tailing. This finding suggests that disorder does not constrain the long-term potential of QD solar cells.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
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DOI of Published Version
https://doi.org/10.1021/acsenergylett.7b00923
