Back contact and transparent electrode optimization for flexible chalcopyrite thin film solar cells

High conversion efficiency, long term stability, low production costs are among the critical issues in the photovoltaic technology. Spray pyrolyzed flexible Cu-based photovoltaics have great opportunities for fulfilling these requirements. In this thesis, CuInS2/In2S3 heterojunction thin film solar cells have been fabricated on flexible substrates -Upilex® and stainless steel foil substrates- by spray pyrolysis technique. MW and atmospheric plasma treatments have been studied systematically before deposition of Mo back contacts. In order to derive large area solar cells without heavy efficiency losses, critical P1, P2 and P3 scribing processes are essential for structuring the photovoltaic cells. With this motivation, P1 scribing processes have been studied systematically using ns and fs fiber lasers. In the case of stainless steel foils, the deposition of barrier layers is required in order to prevent diffusion of iron and other undesired metal atoms. Al2O3 is preferred as a barrier layer due to its unique properties among others. Effects of the barrier layer thickness and thermal annealing processes on the performance of solar devices have been studied. Moreover a novel structure very thin TCO layers -AZO/metal/AZO structure- has been designed for spray pyrolyzed CuInS2/In2S3 heterojunctions. Various types of metals have been studied in AZO/metal/AZO structure to investigate the effect of material selection on TCO quality and device performance. As a result, design and optimization of back contacts and transparent electrodes was performed and effect of processing conditions on both rigid on flexible substrates analyzed deeply. Keywords: Flexible solar cells, barrier layer, Mo back contact, laser scribing, AZO/metal/AZO