Cu 2 ZnSnS 4 nanocrystals (NCs) were synthesized via a low-cost one-pot method. The recipe was optimized by using photoelectrochemical measurements of NC films in contact with a methyl viologen solution. Non-stoichiometric copper-rich and zinc-poor starting molar ratios provided the best overall photovoltaic effect.Other analytical techniques were used to further identify the NC composition, topography and crystallinity. The oxidation states were found to be 1+, 2+, 4+ and 22 for copper, zinc, tin and sulphur, respectively.
Copper indium disulphide (CIS) nanocrystals (NCs) were prepared using a one-pot synthesis. The stoichiometry was optimized based on its current density as measured by photoelectrochemical (PEC) experiments at interfaces between NC films deposited on ITO and 0.1 M methyl viologen dichloride (MV(2+)) solution. This method also offers insight into the kinetics of the photoreaction. A copper poor sulphur rich starting ratio was found to produce a copper-rich, indium-poor and slightly sulphur rich material. Further NC characterization was performed with SEM and TEM to investigate the morphology and crystallinity of the 30-70 nm NCs. The oxidation states of the individual elements were determined to be I, III, and 2- for Cu, In and S, respectively. Characteristics of optimal as-prepared NCs were found to be compatible among high functioning absorbing layers.
Photovoltaics based on inorganic thin film absorber layers such as CuInS 2 (CIS) are showing promise in overcoming the increasing energy demand. There are, however, challenges that CIS presents before it can be considered cost effective. A typical synthesis employs a high temperature (∼500 • C) annealing step with a H 2 S atmosphere, which can significantly raise the cost of the photovoltaic devices. In this work we report a relatively low temperature, H 2 S free annealing step (250 • C) that produced a photocurrent enhancement in the CIS nanocrystal film based on the comparison of respective photoelectrochemical measurements. Investigations into the effects of annealing on the morphology, composition, crystallinity and temperature of degradation of the film were carried out. A thin CdS buffer layer can provide photocurrent enhancement of the CIS layer, but it is typically added after annealing because temperatures above 300 • C will degrade optical properties. The low annealing temperature allowed for CIS and the CdS buffer layer to be annealed together, which produced a further photocurrent density enhancement. The combination of a low temperature annealing along with a large photocurrent enhancement of the CIS/CdS bi-layer could help to improve efficiency in the full device fabrication while still keeping costs low.
CuInS 2 (CIS) nanocrystals (NCs) prepared optimally via a one-pot solvothermal method exhibit a high absorption coefficient and an ideal band gap for solar cell light-absorbing materials. We find that the initial Cu/In ratio in the synthesis determines the final composition of CIS and this further dictates the photoelectrochemical performance of the CIS NC films. X-ray absorption near edge spectroscopy excludes the presence of a secondary phase and suggests a difference in surface band bending and in ligand-CIS interaction. These findings will aid optimizing the design of CIS NC films to achieve the highest possible photovoltaic efficiency.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.