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Direct Imaging of Cl‐ and Cu‐Induced Short‐Circuit Efficiency Changes in CdTe Solar Cells
Author(s) -
Poplawsky Jonathan D.,
Paudel Naba R.,
Li Chen,
Parish Chad M.,
Leonard Donovan,
Yan Yanfa,
Pennycook Stephen J.
Publication year - 2014
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201400454
Subject(s) - materials science , cadmium telluride photovoltaics , grain boundary , scanning transmission electron microscopy , transmission electron microscopy , scanning electron microscope , open circuit voltage , short circuit , optoelectronics , solar cell , analytical chemistry (journal) , crystallite , nanotechnology , voltage , composite material , electrical engineering , chemistry , metallurgy , microstructure , engineering , chromatography
To achieve high‐efficiency polycrystalline CdTe‐based thin‐film solar cells, the CdTe absorbers must go through a post‐deposition CdCl 2 heat treatment followed by a Cu diffusion step. To better understand the roles of each treatment with regard to improving grains, grain boundaries, and interfaces, CdTe solar cells with and without Cu diffusion and CdCl 2 heat treatments are investigated using cross‐sectional electron beam induced current, electron backscatter diffraction, and scanning transmission electron microscope techniques. The evolution of the cross‐sectional carrier collection profile due to these treatments that cause an increase in short‐circuit current and higher open‐circuit voltage are identified. Additionally, an increased carrier collection in grain boundaries after either/both of these treatments is revealed. The increased current at the grain boundaries is shown to be due to the presence of a space charge region with an intrinsic carrier collection profile width of ≈350 nm. Scanning transmission electron microscope electron‐energy loss spectroscopy shows a decreased Te and increased Cl concentration in grain boundaries after treatment, which causes the inversion. Each treatment improves the overall carrier collection efficiency of the cell separately, and, therefore, the benefits realized by each treatment are shown to be independent of each other.