Abstract
The highest efficiency Cu(In,Ga)Se2(CIGS) thin film solar cells have reached 20%. However, the indium and gallium are rare elements in the crust. A promising quaternary semiconductor Cu2ZnSnS4(CZTS) has been proposed to replace CIGS. CZTS is composed of four earth abundant elements, and has some advantages such as high absorption coefficient, direct band gap of 1.5eV, and nontoxic material. The highest CZTS device was fabricated by the solution based hydrazine process. However, hydrazine is a vary toxic and unstable compound, so we choose the hot injection method to synthesize CZTS nanoparticles. We have successfully synthesized high quality CZTS nanoparticles by the hot injection method, and we discussed the CZTS growth mechanism via tuning reaction conditions. We used TEM to observe the size of different nanoparticles, and explained its nucleation and growth mechanism by LaMer model. We also measured CZTS by using XRD and Raman spectrum to identify its structures and phases, and we found that different crystallinity in different reaction condition. Different from other hot injection methods, we used slow injection synthesis to get the high quality CZTS, and we proposed a possible reason to explain why the CZTS nanoparticles possessed different cystallinity. Ostwald ripening and oriented attachment are two mechanisms which may result in different crystallinity during the growth. Moreover, we also observed wurtzite and kesterite CZTS would coexist in the hot injection synthesis.