Layer In Thin Film Solar Cells Research Articles

The distribution of impurities in the interfaces and window layers of thin-film solar cells

We report a systematic multielement study of impurities in CdS window layers by dynamic and quantitative secondary-ion-mass spectrometry (SIMS) with high depth resolution. The study was carried out on CdTe∕CdS solar cell structures, with the glass substrate removed. The analysis proceeded from the transparent conductive oxide free surface to the CdTe absorbing layer with a view to examining the influence of the CdCl2 heat treatment on the distribution and concentration of impurities in the structures. Special attention was paid to the impurities present in the CdS window layer that may be electrically active, and therefore affect the characteristics of the CdTe∕CdS device. It was shown that Cl, Na, and Sb impurities had higher concentrations in CdS following cadmium chloride (CdCl2) heat treatment while Pb, O, Sn, and Cu conserved the same concentration. Furthermore, Zn, Si, and In showed slightly lower concentrations on CdCl2 treatment. Possible explanations of these changes are discussed and the results compared with previous SIMS measurements from the “back wall” (i.e., from the CdTe free surface through the glass substrate) obtained from the same structures.

Efficiency enhancement of Cu(In,Ga)Se2 solar cells due to post-deposition Na incorporation

Cu(In,Ga)Se 2 (CIGS) absorber layers for thin-film solar cells were grown without sodium. Na was diffused into some of the absorbers after growth, which led to strongly improved device performance compared with Na-free cells. Efficiencies of 13.3% and 14.4% were achieved at substrate temperatures as low as 400 and 450 °C, respectively. With the post-deposition treatment, the effects of Na on CIGS growth are excluded, and most of the Na is expected to reside at grain boundaries. The dominating cause for Na-induced device improvements might be passivation of grain boundaries.

Effects of post-deposition treatment on the PL spectra and the hydrogen content of CuInS 2 absorber layers

CuInS 2 absorber layers for thin-film solar cells are examined in this work. The influence of post-deposition annealing in hydrogen and oxygen atmosphere is studied by means of photoluminescence (PL) and nuclear reaction analysis (NRA). The intensity of a PL peak at 1.445 eV can be drastically influenced by post-deposition treatments. This transition is ascribed to the donor-acceptor pair recombination between a sulfur vacancy and a copper vacancy. From the measurements, a simple defect model is deduced which assumes the occupation of sulfur vacancies by oxygen. The sulfur vacancy can be activated by hydrogen annealing and passivated by oxygen annealing.

A first study of radiation damage due to oxygen implantation in CuInSe 2 single crystals

Ion beam channelling has been observed for the first time in 〈110〉 oriented CuInSe 2 single crystals grown by the vertical Bridgman technique. CuInSe 2 is particularly of interest since it is used as an absorber layer in thin-film solar cells, the efficiency of which is optimised by annealing in oxygen. For this reason a first study of oxygen implantation using single crystals and the RBS channelling technique has been made. The implant energy was 40 keV and the implant fluences ranged from 5 × 10 14 to 10 16 atoms cm −2. Data is presented showing a buildup in radiation damage with respect to increasing implant fluence. This shows a general increase in the dechannelling level over the range of the incident oxygen ions as well as an increase in the near surface damage. Preliminary results of the anneal behaviour of the damage are also reported.

Structural and Electrical Properties of Chemical-Solution-Deposited CdS Films for Solar Cells

The structural and electrical properties of CdS films prepared by chemical-solution deposition have been studied. As-deposited films have about 0.4 µm thickness, a grain size of about 0.3 µm and consist of the coalesence of columnar structure. The dark resistivity of more than 104 Ωcm of as-deposited films decreased by about three orders of magnitude to about 10 Ωcm upon annealing in N2 atmosphere at 300–500°C for 20 minutes. The decrease in resistivity was caused by an increase in electron concentration. The resistivity of annealed CdS films was low enough to use as a window layer of thin-film solar cells.

Cadmium-sulphide/copper-sulphide thin-film solar cells: review of methods of producing the CdS and Cu2S layers

The methods that have been used successfully for the production of cadmium-sulphide layers in thin-film solar cells are described. The structural, optical and electrical properties of the resulting layers are discussed and related to the properties required in a high-efficiency thin-film solar cell. A description is also given of some less commonly used methods that might be developed into successful techniques for the production of large-area low-cost solar cells