Abstract
Recent improvements in CdTe thin film solar cells have been achieved by using CdTe1−xSex as a part of the absorber layer. This review summarizes the published literature concerning the material properties of CdTe1−xSex and its application in current thin film CdTe photovoltaics. One of the important properties of CdTe1−xSex is its band gap bowing, which facilitates a lowering of the CdTe band gap towards the optimum band gap for highest theoretical efficiency. In practice, a CdTe1−xSex gradient is introduced to the front of CdTe, which induces a band gap gradient and allows for the fabrication of solar cells with enhanced short-circuit current while maintaining a high open-circuit voltage. In some device structures, the addition of CdTe1−xSex also allows for a reduction in CdS thickness or its complete elimination, reducing parasitic absorption of low wavelength photons.
Highlights
With a global drive towards renewable energies, photovoltaics is an increasing part of global energy supply
Close space sublimation is performed at higher temperatures than high-vacuum deposition or sputtering, and in CdTe it results in very large grains
CdTe1−x Sex thin films measured with different methods, as well as one band gap bowing CdTe derived from first-principles DFT calculations, all showing a similar bowing behavior trend
Summary
With a global drive towards renewable energies, photovoltaics is an increasing part of global energy supply. Different research groups have been investigating the use of a CdTe1−x Sex layer towards the front of a CdTe absorber layer, resulting in champion devices with improved JSC due to higher absorption in the low-band gap front layer, while maintaining the VOC from the bulk CdTe [8,12,13,14,15,16,17]. CdCl2 on the absorber and subsequent heating, is needed to recrystallize the absorber layer, resulting in increased CdTe grain size and intermixing of CdS and CdTe as well as modifications in electronic properties leading to enhancement in photovoltaic conversion efficiency [18]. Close space sublimation is performed at higher temperatures than high-vacuum deposition or sputtering, and in CdTe it results in very large grains. The properties of CdTe1−x Sex are expected to depend on deposition parameters as well as CdCl2 treatment conditions
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