Abstract
Amongst several processes which have been developed for the production of reliable chalcopyrite Cu(InGa)Se2 photovoltaic absorbers, the 2–step metallization–selenization process is widely accepted as being suitable for industrial–scale application. Here we visualize the detailed thermal behavior and reaction pathways of constituent elements during commercially attractive rapid thermal processing of glass/Mo/CuGa/In/Se precursors on the basis of the results of systematic characterization of samples obtained from a series of quenching experiments with set-temperatures between 25 and 550 °C. It was confirmed that the Se layer crystallized and then melted between 250 and 350 °C, completely disappearing at 500 °C. The formation of CuInSe2 and Cu(InGa)Se2 was initiated at around 450 °C and 550 °C, respectively. It is suggested that pre-heat treatment to control crystallization of Se layer should be designed at 250–350 °C and Cu(InGa)Se2 formation from CuGa/In/Se precursors can be completed within a timeframe of 6 min.
Highlights
One of the major issues present in a 2–step process, such as metallization and selenization, is the poor adhesion of CIGS to the Mo layer
The detailed thermal behavior and reaction pathways of constituent elements during RTP of CuGa/In/Se precursors have been visualized based on the results of a systematic characterization of samples obtained from a series of quenching experiments
A detailed look at the thermal behaviour of a Se layer and CuGaIn intermetallic phases was achieved through systematic investigation by a diverse range of characterization techniques
Summary
One of the major issues present in a 2–step process, such as metallization and selenization, is the poor adhesion of CIGS to the Mo layer. This is presumably due to volume expansion, caused by a reaction of Se with the CuGaIn precursor to form a chalcopyrite CIGS structure[6]. In the precursor structure of Mo/Cu–Ga–In/Se it is believed that the crystallization of amorphous Se layer is accompanied by significant volume change, subsequently resulting in mechanical stress of www.nature.com/scientificreports/. The metal precursor[13,14] This subsequently results in poor adhesion of the CIGS layer to Mo, as evidenced by the delamination of CIGS layers from Mo after selenization and/or sulfurization. Particular attention was given to observing the behavior of Se and the intermixing of Ga–In
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