Growth of Copper Zinc Tin Sulfide Thin Films by Wet Chemistry Routes; as a light absorber Layer in CIGS Based Thin Film PV Technology

Abstract

Quaternary semiconducting compound based on the kesterite structure Cu2ZnSnS4(CZTS) has found a renewed interest as a prospective candidate to overtake the conventional light absorber layers such as Cu(In,Ga)Se2 (CIGS) and CdTe. CZTS being a direct band gap material with a range of 1.4-1.5eV and a large absorption coefficient value over 104cm-1, it is one of the most potential applicant as p-type semiconductor material in hetero-junction PV technology. Also, CZTS material comprises of earth abundant, non-toxic and low-cost elements. These quaternary compounds are based on Zinc-blende comprised structures where the complexity related with multi-component system leads towards the difficulties in growth, characterization, and application of this material. The aim of this study was to develop pure CZTS thin films to tackle the reported issue of secondary phase inclusion. Further attempts were made to produce crack free films with average distributed grains of uniform size by making processing parametric study. We introduced a new approach of CZTS nanoparticles doped liquid processed CZTS thin films and also the fabrication of binder based CZTS thin films to overcome the cracks. In this present study, a synthesis of nanoparticles with that of thin films deposition was made for CZTS material where we targeted at the wet chemistry methodologies for its synthesis by keeping the low cost fabrication aspect in mind. Firstly, the liquid processed CZTS thin films were based on the hybrid approach of particle and solution precursors, while the 2nd technique was based on colloidal method. Hydrazine was used as solvent and a complexing agent in very first method, while for second method; oleylamine was used as a solvent and a surfactant as well. A no of approaches were used to have modified results for optimized compact films so to have a best combination of optical and electrical properties of coated films. For analyzing crystallinity and phase purity; X-ray diffractrometer (XRD) was used. All films were oriented in characteristic (112) plane while showing polycrystalline behavior in case of particles. For surface morphological properties investigation, scanning electron microscopy (SEM) was the analyzing tool. Hall Effect Measurement System was used for electrical properties investigation and optical properties were investigated by the use of spectrophotometer. We synthesized three series of nanoparticles with different particle size range by observing an effect of a specific processing parameter and further investigation was made with the materialization of Quantum confinement. The morphological analysis made by SEM showed uniformly shaped spherical nanoparticles and the average size distribution of particles was ranging from 6.39-42.86 nm. An initial resistance value in the range of 104-107(Ωcm) was dropped to a value of 100-103(Ωcm) range with a doping approach.