POLYCRYSTALLINE THIN FILM SOLAR CELLS:Present Status and Future Potential

Abstract

Polycrystalline thin film solar cells based on copper indium diselenide (CuInSe 2) and its alloys and cadmium telluride (CdTe) appear to be the most promising candidates for largescale application of photovoltaic energy conversion because they have shown laboratoryefficiencies in excess of 15%. Heterejunction devices with n-type cadmium sulfide (CdS) films show very low minority carrier recombination at the absorber grain boundaries and at the metallurgical interface which results in high quantum efficiencies. Open circuit voltages of these devices are relatively low owing to the recombination in the space charge region in the absorber. Further improvement in efficiency can be achieved by reducing this recombination current, especially in devices based on CuInSe 2 and its alloys. Low-cost manufacturing of modules requires better resolution of a number of other technical issues. For modules based on CuInSe 2 and its alloys, the role of Na and higher deposition rates on device performance need to be better understood. In addition, replacing the chemical bath deposition method for CdS film deposition with an equally effective, but more environmentally acceptable process are needed. For modules based on CdTe, more fundamental understanding of the effect of chloride/oxygen treatment and the development of more reproducible and manufacturable CdTe contacting schemes are necessary.

Self-passivation rule and structure of CdTe Σ3 (112) grain boundaries

“…Cl concentrating at GBs was deservedly considered as the most important dopant to cure the GBs' defect levels. 6,21,22,23 We show that the Cl dopant in these new GB structures 21,23 induces ntype levels, contributing to the separation of electron-hole pairs, 22,24,25 while the Cd dopant, whose role was neglected in previous studies, facilitates the formation of selfpassivating GBs that enhance the photovoltaic efficiency. These results change the conventional picture about how the CdCl2 post-treatment improves the photovoltaic efficiency of polycrystalline CdTe solar cells, and also manifest that the previous studies on the most stable Σ3 GBs in a series of semiconductors should be revisited.…”

Development of thin‐film Cu(In,Ga)Se2 and CdTe solar cells

“…Comprehensive reviews of CdTe solar cell technology are available. 121,122 The CdCl 2 treatment of CdTe Independent of the growth process, as-deposited CdTe cells exhibit poor electrical performance after growth. However, special annealing treatments significantly improve the cell efficiency, in some cases the increment is up to three times the initial value.…”

Study of the structural and photoluminescence properties of CdTe polycrystalline films deposited by close-spaced vacuum sublimation

“…Up to date high efficiency (16.5%) of CdTe-based solar cells have been achieved [2,3]. However, the theoretical estimations of possible photovoltaic solar energy conversion into electricity for CdTe are of about 28% [4].…”