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Strategies for Thinning Graded Buffer Regions in Metamorphic Solar Cells and Performance Tradeoffs

Journal Article · · IEEE Journal of Photovoltaics
 [1];  [1];  [1];  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
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Compositionally graded buffers (CGBs) have enabled the development of inverted metamorphic (IMM) multijunction solar cells that contain three or more junctions and exhibit record efficiencies. Typically, the CGB is grown thick with a constant grading rate, because this is the most straightforward way to minimize the threading dislocation density (TDD) in device active regions. The CGB growth represents a significant expense, in terms of materials consumption and capital cost, however, hampering the economic viability of metamorphic devices. This work explores strategies for thinning Ga1-xInxP CGBs from GaAs to InP while minimizing performance loss, as evaluated by the open-circuit voltage (VOC) of ~0.74 eV Ga0.47In0.53As solar cells. Using the Ga1-xInxP CGB as a model, we demonstrate that slower grading is necessary in certain regions of the grade where dislocation nucleation rates are higher. Grading must be more gradual in these regions to suppress threading dislocation density. Grading rates can be increased in non-critical areas where dislocation nucleation is lower, permitting a thinner buffer. We demonstrate the relationship between VOC and TDD, establishing tradeoffs between thickness and performance. Through careful design, we demonstrate a CGB with a 40% thickness reduction (2 im) achieved with a VOC decrease of only 6.3% (21 mV).
Research Organization:
National Renewable Energy Laboratory (NREL), Golden, CO (United States)
Sponsoring Organization:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
Grant/Contract Number:
AC36-08GO28308
OSTI ID:
1461854
Report Number(s):
NREL/JA-5900-70796
Journal Information:
IEEE Journal of Photovoltaics, Journal Name: IEEE Journal of Photovoltaics Journal Issue: 5 Vol. 8; ISSN 2156-3381
Publisher:
IEEECopyright Statement
Country of Publication:
United States
Language:
English

Cited By (1)

Printed assemblies of microscale triple‐junction inverted metamorphic GaInP/GaAs/InGaAs solar cells journal March 2019

Figures / Tables (8)

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Related Subjects

14 SOLAR ENERGY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
III-V semiconductor materials
gallium arsenide
indium phosphide
lattices
photovoltaic cells
strain
switches