ELECTRICAL CHARACTERISTICS OF Cu(In,Ga)Se_2 THIN FILMS SOLAR CELLS ON METALLIC FOIL SUBSTRATES

摘要

Flexible thin-film solar cells offer distinct advantages over cells on rigid glass substrates, but their efficiency is yet somewhat lower. When using metallic foil substrates, diffusion of impurities from the metal substrate to the CIGS cell should be avoided or be under control. Here the electrical characteristics of thin film CIGS solar cells on metallic substrate foils are studied in order to assess the influence of the substrate on the internal operation of the solar CIGS cell. We therefore characterised the cells by room temperature I-V, C-V, C-f, QE(λ) and temperature dependent I-V-T, C-V-T, C-f-T measurements. The efficiency of the best cells studied is in the 13% range. The apparent doping density profile N_A(x), deduced from room temperature C-V measurements, is correlated with the nature of the barrier/contact layers. N_A(x) is in the 10~(16) cm~(-3) range, and increasing towards around 2×10~(17) cm~(-3) towards the junction, possibly be due to indium vacancies near the heterointerface This was further evidenced by studying the temperature dependence of C-f-T measurements. Analysis of the temperature dependent V_(oc) and dark I-V curves showed that the dominant recombination is in the CIGS bulk.