Swapnil Deshmukh1 David Rokke1 Rakesh Agrawal1

1, Purdue University, West Lafayette, Indiana, United States

Low cost and large-scale production of semiconducting materials requires development of solution processing routes. While developing such solution processing routes for photovoltaic systems, it is also important to achieve sufficient efficiencies of photovoltaic devices which will ultimately reduce the cost of power generation.
Numerous solution processing routes have been tried for fabricating various semiconducting films for solar energy conversion. Amongst which, Hydrazine has shown highest conversion efficiencies for materials like CIGS and CZTS. However, because of its explosive and carcinogenic nature, it is not feasible to use this chemical in any scale up production. On the other hand, amine-thiol system which is safer than Hydrazine has shown promising results in dissolving array of metals, metal salts, oxides, chalcogenides. Even though devices made with amine-thiol system have demonstrated promising efficiencies, the hydrocarbon chains in amine and thiol species results in formation of carbonaceous fine grain layer in the final film which affects the performance of photovoltaic devices.
Herein, we present a novel approach in utilizing amine-thiol chemistry for film fabrication. Understanding amine-thiol chemistry using various analytical techniques has enabled us in fabricating better quality films. This presentation will exclusively focus on fabrication of such two semiconducting thin film materials viz. CISe and Se-Te alloy. Amongst which, CISe is a low bandgap material and is of great interest for its application in fabrication of tandem solar architectures with high band gap materials like perovskite. We will discuss the effect of various precursor selection and various selenization conditions on CISe film quality and also will demonstrate the fabrication of working device from CISe system with more than 11% efficiency.
Along with novel approach for fabricating conventional material like CISe, we will also discuss our work in synthesizing a novel thin film alloy of Se and Te for photovoltaic application. While people have fabricated working devices with selenium as an absorber material for indoor applications, we will demonstrate an alloying process of Se with Te to tune the bandgap of the absorber material. Our understanding of chalcogen dissolution mechanism in amine-thiol system has made it possible to alloy two chalcogens to form crystalline phase material. This presentation will include synthesis as well as thin film fabrication from Se-Te alloy followed by primary attempt of making a working photovoltaic device with various architectures.
In conclusion, we have come up with better understanding of amine-thiol system which enabled us to develop novel approach for its use in better quality semiconducting films. The results of which are applicable to the synthesis of nanoparticles and films of a vast array of chalcogenides including Cu2S, WSe2, SnS, SnSe, FeS2, CZTS and other Kesterites.