期刊
SOLAR ENERGY MATERIALS AND SOLAR CELLS
卷 209, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.solmat.2020.110468
关键词
CdTe solar cell; Carrier concentration; As-doping; Scanning capacitance microscopy (SCM); Kelvin probe force microscopy (KPFM); Cathodoluminescence (CL)
资金
- U.S. Department of Energy [DE-AC36-08GO28308]
- Alliance for Sustainable Energy, LLC
- U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Office
We report nanometer-scale hole-density imaging in As-doped CdTe films by scanning capacitance microscopy (SCM). The hole-density profiling is validated by contrasting a CdTe cross-section sample made by molecular-beam epitaxy with systematically increased As doping in a staircase pattern over the range of 10(15)-10(18)/cm(3) within a single film. In polycrystalline films, the carrier distribution is significantly nonuniform, with inhomogeneity ranging from several hundred nm to several mu m and hole density varying by one order of magnitude (low 10(16) to low 10(17)/cm(3)). This nonuniformity is distributed randomly, independent of the grain structure and grain boundaries (GBs). Kelvin probe force microscopy (KPFM) maps the surface potential and is correlated to cathodoluminescence (CL) and SCM by imaging over identical areas. Higher potential and lower CL intensity are found on GBs but not by SCM contrast; this indicates positive GB charging and recombination, but not GB-specific hole-density changes. The overall KPFM potential image is in rough agreement with the SCM carrier distribution and indicates band-edge potential fluctuations. Nonuniform carrier concentration, potential fluctuations, and defect recombination can all cause voltage and performance loss in As-doped CdTe solar technology.
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