On the process of chalcopyrite CuInS2 and Cu2ZnSnS4 solar absorber layers

Abstract

The objective of this research is the growth and characterization of the Chalcopyrite-like solar absorption layer and the development of sulfurization process Our studies include CuInS2 and Cu2ZnSnS4 materials There were numbers of methods to grow (for/of growing) CuInS2 thin films The most common seen method is two-step process in which the precursor is prepared first and then subsequently removed into a reactive furnace for further sulfurization process using sulfur powder or H2S gas as sulfur sources In our research the precursors of CIS and CZTS thin film were made via a non-vacuum process The precursor film was put into a quartz tube under 10% H2S/Ar atmosphere During the sulfurization process the main parameters affecting the resulted CuInS2 and Cu2ZnSnS4 thin films were layered structure of precursors sulfurization temperature and sulfurization pressure In studies of CuInS2 the precipitates were then calcined at different temperatures for different durations Depending on the type of salt and calcination condition single phases Cu2In2O5 and CuInGaO4 or the mixture of both oxides were obtained Reaction mechanisms are proposed to explain the formation of the oxides obtained For the formation of CuInS2 (CIS) coatings sulfurization of single crystalline Cu2In2O5 nanoparticles (NPs) Cu2In2O5 NPs were synthesized using a chemical route Thus formed NPs were applied to a Mo-coated glass substrate by a doctor-blading technique After the doctor-blading coatings were sulfurized under 560 torr of H2S at various temperatures Selected doctor-bladed samples were heat treated at 430 °C in air for 30 min for the removal of carbon residual prior to the sulfurization During the sulfurization Cu2S (melting point 435 °C) was used as the sintering aid The weight ratio of Cu2S to Cu2In2O5 was varied The effect of Cu2S on the CIS crystalline structure was explored using Raman analysis It was found that Cu2S not only improves the sintering but also promotes the formation of desired CIS-chalcopyrite structure and reduces the impurity phase (CuIn5S8 and CH-CuInS2) in the resulting CIS coatings Finally at 500 torr 450~550℃ CuInS2 (Cu/In ratio: 1 8) will be formed from oxide precursor the energy gap is 1 30~1 38 In Cu2ZnSnS4 (CZTS) precursor layer was prepared using sequential electrodeposition of individual Cu Zn and Sn in different orders In each stacking order the Cu/(Sn+Zn) ratio was varied Detailed growth path is therefore reported We also demonstrate that by controlling the stacking order and the Cu/(Sn+Zn) ratio CZTS with a phase purity as high as 93% can be obtained Finally selected CZTS film with high purity Cu2ZnSnS4 will be studied the phase transformation and the formation path form metal to Cu2ZnSnS4 phase will be discussed In SEM analysis there is 150 nm film growing on the top of Cu-Sn-Zn precursor at 375 ℃ After XRD and Raman analysis the mixture phase of ZnS Cu2SnS3 and Cu2ZnSnS4 formed at 375 ℃ Finally we found Cu2ZnSnS4 formed on the top of ZnS and Cu2S phase at 400 ℃ via TEM analysis

Date of Award	2015 Jan 20
Original language	English
Supervisor	Jyh-Ming Ting (Supervisor)