Review of CdTe1−xSex Thin Films in Solar Cell Applications

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.

Wide Band Gap Chalcogenide Semiconductors

“…Other common n-type dopants include Ga Cd , Al Cd , and Cl S , , while p-type dopants include Cu Cd (up to 2 S cm –1 , likely due to impurity band or hopping conduction) , and Bi S (up to 10 –1 S cm –1 and mobilities of 3 cm 2 V –1 s –1 ) . Compared to CdS, CdSe and CdTe have lower band gaps (<2.0 eV) , and are reviewed extensively elsewhere, − though we note they can also act as substitutional partners with other chalcogenides to form wide-gap semiconductor alloys (see Figure ).…”

Chlorine passivation of grain boundaries in cadmium telluride solar cells

“…Low cost is achieved, in part, by using a rapid sublimation process to deposit the polycrystalline thin-film CdTe absorber [1]. This has been modified recently by introducing selenium to the front of the cell in a CdSeTe alloy [2][3][4]. In comparison with single-crystal devices, the deposition of the polycrystalline absorber introduces a range of defects, including grain boundaries (GBs), which place a limit on the conversion efficiency [5].…”

Scientific complications and controversies noted in the field of CdS/CdTe thin film solar cells and the way forward for further development

“…Therefore, all the experimentally observed results were analysed and interpreted as a simple p-n hetero-junction [1][2][3][4][5][6][7][8]. In parallel, theoretical calculations and simulations were also carried out for this solar cell assuming principles of p-n junction diodes [9][10][11][12]. This is a classic example of following the same ideas in scientific research without critically testing the existing wisdom.…”