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Title: The roles of carrier concentration and interface, bulk, and grain-boundary recombination for 25% efficient CdTe solar cells

Abstract

CdTe devices have reached efficiencies of 22% due to continuing improvements in bulk material properties, including minority carrier lifetime. Device modeling has helped to guide these device improvements by quantifying the impacts of material properties and different device designs on device performance. One of the barriers to truly predictive device modeling is the interdependence of these material properties. For example, interfaces become more critical as bulk properties, particularly, hole density and carrier lifetime, increase. We present device-modeling analyses that describe the effects of recombination at the interfaces and grain boundaries as lifetime and doping of the CdTe layer change. The doping and lifetime should be priorities for maximizing open-circuit voltage (V oc) and efficiency improvements. However, interface and grain boundary recombination become bottlenecks for device performance at increased lifetime and doping levels. In conclusion, this work quantifies and discusses these emerging challenges for next-generation CdTe device efficiency.

Authors:
 [1];  [1];  [1]; ORCiD logo [1];  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
OSTI Identifier:
1371645
Report Number(s):
NREL/JA-5K00-67610
Journal ID: ISSN 0021-8979; JAPIAU
Grant/Contract Number:
AC36-08GO28308
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 121; Journal Issue: 21; Journal ID: ISSN 0021-8979
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; doping; II-VI semiconductors; hole density; grain boundaries; materials properties

Citation Formats

Kanevce, A., Reese, Matthew O., Barnes, T. M., Jensen, S. A., and Metzger, W. K. The roles of carrier concentration and interface, bulk, and grain-boundary recombination for 25% efficient CdTe solar cells. United States: N. p., 2017. Web. doi:10.1063/1.4984320.
Kanevce, A., Reese, Matthew O., Barnes, T. M., Jensen, S. A., & Metzger, W. K. The roles of carrier concentration and interface, bulk, and grain-boundary recombination for 25% efficient CdTe solar cells. United States. doi:10.1063/1.4984320.
Kanevce, A., Reese, Matthew O., Barnes, T. M., Jensen, S. A., and Metzger, W. K. 2017. "The roles of carrier concentration and interface, bulk, and grain-boundary recombination for 25% efficient CdTe solar cells". United States. doi:10.1063/1.4984320.
@article{osti_1371645,
title = {The roles of carrier concentration and interface, bulk, and grain-boundary recombination for 25% efficient CdTe solar cells},
author = {Kanevce, A. and Reese, Matthew O. and Barnes, T. M. and Jensen, S. A. and Metzger, W. K.},
abstractNote = {CdTe devices have reached efficiencies of 22% due to continuing improvements in bulk material properties, including minority carrier lifetime. Device modeling has helped to guide these device improvements by quantifying the impacts of material properties and different device designs on device performance. One of the barriers to truly predictive device modeling is the interdependence of these material properties. For example, interfaces become more critical as bulk properties, particularly, hole density and carrier lifetime, increase. We present device-modeling analyses that describe the effects of recombination at the interfaces and grain boundaries as lifetime and doping of the CdTe layer change. The doping and lifetime should be priorities for maximizing open-circuit voltage (Voc) and efficiency improvements. However, interface and grain boundary recombination become bottlenecks for device performance at increased lifetime and doping levels. In conclusion, this work quantifies and discusses these emerging challenges for next-generation CdTe device efficiency.},
doi = {10.1063/1.4984320},
journal = {Journal of Applied Physics},
number = 21,
volume = 121,
place = {United States},
year = 2017,
month = 6
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on June 6, 2018
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Citation Metrics:
Cited by: 7works
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  • Cited by 7
  • The atomic structure and composition of grain boundaries in CdCl2 treated CdTe solar cells have been determined with aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy. A high fraction of Te in the grain boundary regions has been substituted by Cl. Density functional calculations reveal the origin of such segregation levels, and further indicate the GBs are likely inverted to n-type, establishing local P-N junctions, which help to separate electron-hole carriers. The results are in good agreement with electron beam induced current observations of high collection efficiency at grain boundaries.
  • The bulk Shockley-Read-Hall carrier lifetime of CdTe and interface recombination velocity at the CdTe/Mg{sub 0.24}Cd{sub 0.76}Te heterointerface are estimated to be around 0.5 μs and (4.7 ± 0.4) × 10{sup 2 }cm/s, respectively, using time-resolved photoluminescence (PL) measurements. Four CdTe/MgCdTe double heterostructures (DHs) with varying CdTe layer thicknesses were grown on nearly lattice-matched InSb (001) substrates using molecular beam epitaxy. The longest lifetime of 179 ns is observed in the DH with a 2 μm thick CdTe layer. It is also shown that the photon recycling effect has a strong influence on the bulk radiative lifetime, and the reabsorption process affects the measured PL spectrum shape and intensity.
  • This article provides a theoretical investigation of recombination at grain boundaries in both bulk and {ital p}-{ital n} junction regions of silicon solar cells. Previous models of grain boundaries and grain boundary properties are reviewed. A two dimensional numerical model of grain boundary recombination is presented. This numerical model is compared to existing analytical models of grain boundary recombination within both bulk and {ital p}-{ital n} junction regions of silicon solar cells. This analysis shows that, under some conditions, existing models poorly predict the recombination current at grain boundaries. Within bulk regions of a device, the effective surface recombination velocitymore » at grain boundaries is overestimated in cases where the region around the grain boundary is not fully depleted of majority carriers. For vertical grain boundaries (columnar grains), existing models are shown to underestimate the recombination current within {ital p}-{ital n} junction depletion regions. This current has an ideality factor of about 1.8. An improved analytical model for grain boundary recombination within the {ital p}-{ital n} junction depletion region is presented. This model considers the effect of the grain boundary charge on the electric field within the {ital p}-{ital n} junction depletion region. The grain boundary charge reduces the {ital p}-{ital n} junction electric field, at the grain boundary, enhancing recombination in this region. This model is in agreement with the numerical results over a wide range of grain boundary recombination rates. In extreme cases, however, the region of enhanced, high ideality factor recombination can extend well outside the {ital p}-{ital n} junction depletion region. This leads to a breakdown of analytical models for both bulk and {ital p}-{ital n} junction recombination, necessitating the use of the numerical model. {copyright} {ital 1996 American Institute of Physics.}« less