Search

The use of a high resistivity transparent oxides (HRT) onto low resistivity transparent oxides (TCO) has been found to improve the performance of CdS/CdTe solar cells. In this work is presented and discussed a study about the use of a commercial conductive glass with SnO2:F as TCO and SnO2 as resistive transparent oxide as front contact in CdS/CdTe solar cells. The SnO2 was deposited by pneumatic spray pyrolysis and its electrical and optical properties were controlled and optimized by varying the substrate temperature and deposition time with the application of a post thermal treatment in O2 atmosphere. The transfer length method (TLM) was implemented to characterize electrically the SnO2:F/SnO2 as well the SnO2/CdS and SnO2:F/SnO2/CdS interfaces through the resistivity and specific contact resistivity measurements and their dependence on O2 treatment were analyzed. The use of the TCO/buffer layer on the CdS/CdTe solar cell in combination with the thermal treatment proposed in this work for TCO and HRT reduced the front contact/CdS contact resistance in a 10 factor and the solar cell efficiency was improved from 6.4% to 12.2%.

Cu(In, Ga)Se2 (CIGS) and Cu2ZnSnS4 (CZTS) semiconductors are direct band gap materials; when these types of material are used in solar cells, they provide efficiencies of 22.1% and 12.6%, respectively. Most traditional fabrication methods involve expensive vacuum processes including co-evaporation and sputtering techniques, where films and doping are conducted separately. On the other hand, the chemical bath deposition (CBD) technique allows an in situ process. Cu-doped CdS thin films working as a buffer layer on solar cells provide good performing devices and they may be deposited by low cost techniques such as chemical methods. In this work, Cu-doped CdS thin films were deposited using the CBD technique on SnO2:F (FTO) substrates. The elemental analysis and mapping reconstruction were conducted by EDXS. Morphological, optical and electrical properties were studied, and they revealed that Cu doping modified the CdS structure, band-gap value and the electrical properties. Cu-doped CdS films show high resistivity compared to the non-doped CdS. The appropriate parameters of Cu-doped CdS films were determined to obtain an adequate window or buffer layer on CIGS and CZTS photovoltaic solar cells.

In this work, a typical superstrate structure of a CdS/CdTe solar cell has been developed, incorporating a Te p+ region in the CdTe surface as a back contact. The Te region was grown as a nanostructured thin film material on the CdTe surface by employing the close space vapor transport (CSVT) technique. The incorporation of a nanostructured Te p+ region to the typical CdS/CdTe structure increased the efficiency from 4.5%–12%. A strong dependence on the electrical characteristics of the CdTe/metal junction on the morphological properties of the Te p+ region was observed, and an appreciable reduction in the Cu diffusion into the solar cell was measured by secondary ion mass spectrometry (SIMS). Thus, we demonstrate that a nanostructured Te p+ region is the best option to improve the performance of the back contact.