We have investigated the effect of pH on the structural and optical properties of chemical coprecipitated Cu2ZnSnS4 (CZTS) nanoparticles. The CZTS nanoparticles have been successfully synthesized at different pH values ranging from 6 to 9, keeping all other deposition parameters as constant. X-ray diffraction and Raman studies confirmed the Kesterite structure. The powders synthesized at a pH value of 8 exhibited preferred orientation along (112) and (220) with near stoichiometric ratio. The as synthesized nanoparticles exhibited direct band gap of 1.4？eV which is an optimum value for the absorber layer in the fabrication of photovoltaic cells. 1. Introduction In the last five decades, the properties of bulk materials have been investigated and understood in great detail. But now a great deal of research interest has been turned on the preparation and characterization of nanoparticles for their unique size-dependent electrical and optical properties. Nanotechnology has recently attracted more interest in the fields of photovoltaics, electrooptical devices and sensors, and so forth. Traditionally, CuInGaSe2 (CIGS) and CuInSe2 (CIS) have been used as absorber layer in solar cells because of their high conversion efficiency (20%) [1]. But the utilization of these materials in large scale solar cell production could cause an environmental problem due to the toxic nature of selenium and expensive raw materials. To overcome these difficulties, alternative search for absorber layers is still ongoing. Recently the copper zinc tin sulphide (CZTS) nanoparticles have attracted researchers with their unique properties, and they play crucial role in the application of absorber layer in the solar cell. The elements of CZTS are earth abundant, inexpensive, environmental friendly, nontoxic, and pollution-free [2]. CZTS has optimum band gap of？？1.4？eV to 1.5？eV which is suitable for photovoltaic applications [3]. CZTS has high absorption coefficient >104？cm？1 [4]. Theoretical conversion efficiency of CZTS solar cell is 32.2% [5]. The CZTS solar cell exhibits a conversion efficiency of 10% [6]. Only limited work was carried out on the preparation and characterization of bulk CZTS [7–11]. But due to the advantages of nanoparticles, in this present work we are synthesizing CZTS nanoparticles. Among many physical methods [12–15] and chemical methods [16–25], chemical coprecipitation method has great advantages in preparing CZTS nanoparticles due to inexpensive apparatus, low power consumption, nontoxic byproducts, high homogeneous, high flexibility, effective size control,
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