The Synthesis and Photoelectrochemical Applications of Nano Cu2ZnSnSe4 Crystal

Abstract

In this work we report a systematic study of the growth and evolution mechanism of quaternary Cu2ZnSnSe4 (CZTSe) nanocrystals (NCs) in a polyetheramine solvent Pure-phase CZTSe NCs were synthesized by a facile one-pot heating process High-quality CZTSe NCs were easily obtained by mixing the precursors and simply heating them to the reaction temperature Synthesis parameters including reaction temperature reaction time and precursor concentration which influence the morphology size and monodispersity of CZTSe NCs were studied in detail Time- and temperature-dependent experiments were performed to observe the growth of CZTSe NCs The final CZTSe NCs were evolved from triangle-like Cu2Se crystals to pure spherical crystals On the basis of detailed time-dependent shape and elemental composition evaluations a possible asynchronous doping growth and formation mechanism is proposed Moreover the optical and electrical properties of pure CZTSe NCs were also investigated The band gap of CZTSe was approximately 1 57 eV which is close to the optimum value for solar photoelectric conversion The precipitated NCs were redispersed in toluene to form ink solutions for characterization The properties of thin films of these inks were investigated as a function of the chemical compositions of the inks The Cu/(Zn+Sn) ratio of the inks was varied from 0 7 to 1 0 while the Zn/Sn ratio was kept constant at 1 Photodetectors (PDs) with a Au/CZTSe/soda-lime glass structure were fabricated The PD corresponding to a Cu/(Zn+Sn) ratio of 0 70 exhibited excellent photoresponsivity and its dark current was 7 65 × 10?7 A when a bias of 10 V was applied In the chemical applications the sensing membrane of an extended-gate field-effect-transistor (EGFET) pH sensor with CZTSe nanoparticles was fabricated on a glass substrate through a solution-based method The resulting EGFET pH sensors with CZTSe nanocrystals exhibited good sensing performances owing to the large sensing surface-to-volume ratio The pH sensitivity calculated from the linear relation between the drain-source current and the pH value was 7 μA/pH and that calculated from the linear relation between the reference voltage and the pH value was 9 mV/pH By controlling the Zn-to-Sn ratio the resulting CZTSe particle films exhibited a photoresponse of n-type and p-type semiconductor photoelectrodes in an aqueous solution containing NaCl as an electron scavenger The comparison between n-type and p-type CZTSe photoelectrochemical (PEC) property are demonstrated athe pplication of CZTSe thin film photoanodes in PEC results in the value of ηc = 2 81% was found in n-type The lower ηc = 0 42% obtained from p-type CZTSe photoanodes the flat band potential of the n-type and p-type CZTSe in 1 M NaCl were obtained to be -0 55 and 0 48V the net carrier concentration of the n-type and p-type calculated from Mott–Schottky plot were 3 38 x1018 and 2 73 x1018 cm-3 respectively Keyword: Cu2ZnSnSe4; Synthesis; Photoelectrochemical

Date of Award	2014 Jun 17
Original language	English
Supervisor	Shoou-Jinn Chang (Supervisor)