Design and optimisation of process parameters in an in-line CIGS evaporation pilot system

Substantial efforts have been made globally towards improving Cu(In,Ga)Se2 thin film solar cell efficiencies with several organisations successfully exceeding the 20% barrier on a research level using the three-stage CIGS process, but commercial mass production of the three-stage process has been limited due to the technological difficulties of scaling-up. An attempt has been made to identify these issues by designing and manufacturing an in-line pilot production deposition system for the three-stage CIGS process which is capable of processing 30 cm × 30 cm modules. The optimisation of the process parameters such as source and substrate temperature, deposition uniformity, flux of copper, indium, gallium and selenium and thickness control has been presented in this investigation. A simplistic thickness distribution model of the evaporated films was developed to predict and validate the designed deposition process, which delivers a comparable simulation compared with the experimental data. These experiments also focused on the optimisation of the temperature uniformity across 30 cm × 30 cm area using a specially designed graphite heating system, which is crucial to form the correct α-phase CIGS in the desired time period. A three-dimensional heat transfer model using COMSOL Multiphysics 4.2a software has been developed and validated with the help of experimental data.