Controlled Synthesis Of Cadmium Telluride And Lead Sulfide Semiconductor Nanocrystals And Their Photovoltaic Applications

This paper focuses on two nanocrystals with potential photovoltaic applications duringthe author’s master degree. One is the CdTe semiconductor nanocrystals, which blockmaterial bandgap of about1.45eV, belonging to the narrow bandgap material. Theabsorption coefficient of104/cm, is very suitable for photoactive layer of solar cells. Anotheris PbS colloidal quantum dots with the controllable morphology and size, whose quantum sizeeffect is obvious. We can change the absorption edge of PbS quantum dots in the differentranges by adjusting the particle size.Based on our research group studies on CdTe nanocrystals, I deeply studied the effectsof saturated solution of methanol CdCl2treatment and annealing temperature on the preparedITO/CdTe/Al Schottky solar cells. The characterization results of EDS, UV and SEM allshowed that the treatment of methanol saturated solution of CdCl2is in favor of size growthof CdTe thin-film nanocrystalline. AFM and I-V curves all showed that the deviceperformance and film quality were best at350℃annealing temperature. Through optimizingthe preparation conditions consistently, we finally obtained up to4.09%energy conversationefficiency by using saturated solution of methanol CdCl2treatment, and annealing at350℃for40s, with Jsc=12.2mA/cm2，Voc=0.46V and FF=49.4%.The use of the solvothermal method, we successfully synthesized PbS-I, PbS-II, PbS-III,PbS-IV four kinds of quantum dots with different surface ligands by controlling the reactiontemperature and the type of complex ligands. The study showed that the introduction ofcomplex ligands can effectively improve the particle size distribution of PbS quantum dotsand prevent their reunion, achieving controllable synthetic PbS quantum dots. The carbonchain length of the alkyl phosphate in ligand complex greatly affects the size of PbS quantumdot. The longer the carbon chain length is, the larger size of the synthesized quantum dots.The Schottky structure solar cells were prepared by these four PbS quantum dots, one ofwhich is PbS-II quantum dots, showing the best device performance. In order to improve theinterface properties and reduce interfacial defects, we introduced a layer of40nm PEDOT:PSS between the ITO layer and the PbS quantum dot active layer and controlled the thickness of the active layer about200nm, succeeded in preparing high energy conversion of3.72%PbS-II quantum dots Schottky solar cells, with Voc=0.46V, Jsc=12.2mA/cm2, andFF=49.4%, which is roughly equal to the reported highest efficiency.Through introducing the5nm alcohol-soluble polymer PFN between PbS quantum dotsand metal electrodes Al, we slightly improved device performance. We carried out necessaryexploration of the specific mechanisms and it is possible to achieve higher performancethrough further research.