Optical, electrical and photovoltaic characteristics of CdS/CdTe thin film solar cells

In this article, the construction and optical characterisation of indium tin oxide/CdS/CdTe/Al thin film solar cells are presented. The analysis of the optical behaviour of the absorption coefficient (alpha) of both CdTe and CdS thin films, in the absorption region has revealed a direct transition, and the energy gap was estimated as 1.45 and 2.4eV, respectively. Characteristic junction parameters and dominant conduction mechanisms have been obtained. The current transport properties of CdS/CdTe heterojunction solar cells under dark condition, in the temperature range 100-300K, were investigated. The transport mechanism of the solar cells appeared to be thermally assisted tunnelling in the forward bias region. Nearly 16% efficiency is achievable with 0.2eV electron reflector, a 1-mu m absorber layer, a 10(14) cm(-3) hole density, a 1 -ns lifetime, and a 20% optical back reflection. This thin film device has showed a photovoltaic behaviour with a maximum open circuit voltage, V-oc, of about 0.650-0.830 V; short-circuit current density, J(sc), of 22.5mAcm(-2), fill factor, FF, of 0.80 and power conversion efficiency, eta, of 16% to 18% under 100mWcm(-2) white light illumination of the AM 1.5 spectrum.