Structures, optical absorption and electrical properties of pulsed-laser-deposited CuIn0.8Ga0.2Se2 thin films and their use in CIGS/PCBM photovoltaic structures

Abstract

Polycrystalline CuIn0.8Ga0.2Se2 (CIGS) thin films are deposited on ITO-glass substrates at different substrate temperatures by pulsed laser deposition using a Nd:YAG laser. The crystallinity of the as-deposited CIGS films significantly improved as the substrate temperature increased. The experimental results indicate that the ordered defect compound model is also applicable to the CIGS films deposited in these experiments. All the as-deposited CIGS thin films show absorption coefficients of 105 cm−1 magnitude in a wavelength range of 400–900 nm. The CIGS thin films deposited at substrate temperatures lower than 400 °C exhibit n-type conductivity while those deposited at a substrate temperature of 500 °C display p-type conductivity. The CIGS/phenyl-C61-butyric acid methyl ester (PCBM) photovoltaic structure, with a CIGS layer as the only absorber, demonstrates an apparent photovoltaic response with a short circuit current density of 0.389 mA cm−2 and an open circuit voltage of 0.327 V.