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

Abstract

Cadmium telluride-based solar cell is the most successfully commercialised thin film solar cell today. The laboratory-scale small devices have achieved ~ 22%, and commercial solar panels have reached ~ 18% conversion efficiencies. However, there are various technical complications and some notable scientific contradictions that appear in the scientific literature published since the early 1970s. This review paper discusses some of these major complications and controversies in order to focus future research on issues of material growth and characterisation, post-growth processing, device architectures and interpretation of the results. Although CdTe can be grown using more than 14 different growth techniques, successful commercialisation has been taken place using close-space sublimation and electrodeposition techniques only. The experimental results presented in this review are mainly based on electrodeposition. Historical trends of research and commercial successes have also been discussed compared to the timeline of novel breakthroughs in this field. Deeper understanding of these issues may lead to further increase in conversion efficiencies of this solar cell. Some novel ideas for further development of thin film solar cells are also discussed towards the end of this paper.

Electrodeposition of ternary compounds for novel PV application and optimisation of electrodeposited CdMnTe thin-films

“…PEC Cell Measurement for electrical conductivity type. CdTe on its own shows p-type electrical conductivity when grown with Te-richness 16 . Hence, during electrodeposition, CdTe changes its conduction type from p to n, due to the greater incorporation of cadmium at larger cathodic voltages surpassing Te.…”

“…It has been conceptualised by our group that, GBG devices can be constructed based on two approaches in terms of the electronic conduction type of the window material; i) fabricated on n-type window and ii) fabricated on p-type window. Though our current highest efficiency for CdTe-based GBG solar cells are achieved from n-window devices, cells fabricated on p-type windows have a potential to achieve higher performance due to the possibility of producing higher open circuit voltage (V oc ) resulted from a higher potential barrier 15 , 16 . This has been experimentally demonstrated by achieving Voc ≈ 1.17 V with GaAs/AlGaAs and Voc ≈ 1.00 V with Perovskite based solar cells 17 , 18 .…”

The viability of alternative and nontoxic chlorine containing compounds for thermal treatment of ultrathin CdTe (≤1.0 μm) films

“…It has been reported that thermal treatment creates Cd vacancies (V Cd ) that could facilitate the substitution of metal atoms in the Cd sub-lattice (M Cd ). 52,53 Both V Cd and M Cd create acceptor-like energy states located at E v + 0.13 eV and E v + 0.22 eV above the valence band, 54 respectively. Moreover, the thermal treatment also improves the film's crystalline quality as seen in XRD and SEM images in the previous section and also reported elsewhere.…”

Investigation of Electrical Parameters of CdTe Photovoltaic Devices by Computational Analysis

“…[ 4 ] R.H. Bube and others carried out further analysis of CdS/CdTe‐based photovoltaic heterojunction cells and obtained an efficiency value of 8.4%. [ 5 ] In 1980, Tyan Yuan Sheng of Eastman Kodak Company established different fabrication techniques for polycrystalline CdTe‐based solar cells with an efficiency of 8.9%. [ 6 ]…”