Preparation And Photoelectric Properties Study On The Quaternary Chalcogenide Compounds Thin Film

Research in thin film solar cells continues to make substantial progress towards developingcommercially viable low-cost and high-efficiency photovoltaic (PV) devices. Cu(In,Ga)Se2(CIGS) solarcells are among the most promising materials for thin film solar cells due to its high power conversionefficiency and fine stability. However, this compound contains rare and costly metals such as In and Ga,and the band gap is usually not optimal for high efficiency solar cells,that may hinder commerciallyavailable production of CIGSe based solar cells. The Cu2-II-IV-VI4quaternary compound CZTS andCZTSe are considered to be the most promising substitutes for CIGS owing to its direct band gap, highoptical absorption coefficient(>104cm-1) and p-typ e electrical conductivity.Moreover, element Zn and Snare non-toxic,low cost and earth-abundant,which make it suitable for cost-effective and large-scaleproduction of CZTS/CZTSe based solar cells.Nowdays, a high-quality thin film can be fabricated byphysical method,but this preparationconditionis harsh and high costs. The solution based approach have been recently demonstrated as effectivemethod in preparing nanoparticle film. However, this approach used the nanoparticle-based depositiontechnique, which encountered many problems, such as solubility, toxic solvent, long-term stability, yield,ligand exchange, removal of ligands, and mass production.In this work, we present a simple route for thefabrication of CZTS/CZTSe material which involves filmdeposition with in situ nanocrystals synthesis,thereby circumventing the need to first synthesize the NCs and thenperform a ligand exchange. Thesynthetic and film deposition processes are relatively simple compared to thoseof nanoparticles. It utilizessignificantly less toxic solvents and low temperature processability also provides ahigh potential forminimization of environmental impactand cost-reduction.This thesis includes the following main aspects: 1. First, a CZTS precursor solution was obtained by using short-chain butylamineand ethanol assolvent. Then, the CZTS nanocrystal thin film with a thickness of1.5μm was obtained by repeating sevenspin-casting/sintering cycles. The X-ray difraction patterns and Raman spectra revealed that the maindifraction peaks changed after selenization. This is attributed to the expansion of the unit cell volume bythe partial replacement of S with Se. After the selenization at550°C for30min, we obtained a CZTS thinfilm with a dense large grain. We can control the band gap of CZTS by changing selenization time.2. The CZTS solar-cell device was fabricated according to theconventional configuration ofglass/Mo/CZTS/CdS/i-ZnO/ITO/Al. The active area of the as-fabricated device is0.39cm2. The low powerconversion efficiency was due to the difficulty of assembly technology.3. We have presented a novel solution-based in situ synthesis and fabrication method for a CZTSe filmusing DMSO as solvent, which is commercially available and non-toxic. The surface of CZTSe nanocrystalfilm after selenization treatment is rather rough, andwould provide a large internal surface area forelectrocatalytic sites4. DSSCs with CZTSe thin films as low-cost CE were fabricated. A highest solar energy conversionefficiency of7.82%was achieved, which is remarkablysimilar to that of the Pt CE. Photovoltaicmeasurementshowed that the thickness of the film affected the photocurrent density and fill factorremarkably.