4 research outputs found
Stacked Cu1.8S nanoplatelets as counter electrode for quantum dot-sensitized solar cell
It is found that the electrocatalytic activity of Cu2-xS thin films used in quantum dot-sensitized solar cells (QDSSCs) as counter electrode (CE) for the reduction of polysulfide electrolyte depends on the surface active sulfide and disulfide species and the deficiency of Cu. The preferential bonding between Cu2+ and S2-, leading to the selective formation of a Cu1.8S stacked platelet-like morphology, is determined by the cetyl trimethyl ammonium bromide surfactant and deposition temperature; the crab-like Cu-S coordination bond formed dictates the surface area to volume ratio of the Cu1.8S thin films and their electrocatalytic activity. The Cu deficiency enhances the conductivity of the Cu1.8S thin films, which exhibit near-infrared localized surface plasmon resonance due to free carriers, and UV-vis absorption spectra show an excitonic effect due to the quantum size effect. When these Cu1.8S thin films were employed as CEs in QDSSCs, a robust photoconversion efficiency of 5.2% was obtained for the film deposited at 60 °C by a single-step chemical bath deposition method
Phase Transformation and Evolution of Localized Surface Plasmon Resonance in Cu<sub>2–<i>x</i></sub>S Thin Films Deposited at 60 °C
Cu<sub>2–<i>x</i></sub>S (0 ≤ x ≤
1) thin films deposited at low temperatures (<95 °C) have
rich polymorphs due to small differences in Gibbs free energy of formation,
which is critical for understanding their fundamental properties.
In this work, phase transformation from djurleite to covellite is
obtained by simple chemical bath deposition (CBD) without using oxidizing/reducing
agents. Cu<sub>2–<i>x</i></sub>S thin films synthesized
using cetyltrimethylammonium bromide as a surfactant at 60 °C
for different deposition time exhibit red shift in optical absorption
due to quantum size effect and blue shift in localized surface plasmon
resonance in the near-infrared region originating from increased copper
vacancy. The surface morphology of the Cu<sub>2–<i>x</i></sub>S thin films is influenced by the surfactant, which in turn
alters the optoelectronics properties. The preferential bonding between
Cu and S is determined by hydrolysis of thioacetamide to release sulfides
(S<sup>2–</sup>) and disulfides (S<sub>2</sub><sup>2–</sup>) and the kinetics to reduce Cu<sup>2+</sup> to Cu<sup>+</sup> leading
to mixed phase formation and an increase in surface to volume ratio.
Through X-ray photoelectron spectroscopy and X-ray absorption near
edge structure analysis, it is confirmed that both Cu<sup>2+</sup> and S<sup>2–</sup> are reduced with time of deposition and
form covellite Cu–S<sub>2</sub><sup>2–</sup>–Cu
bonds
Phase transition kinetics and surface binding states of methylammonium lead iodide perovskite
We have presented a detailed analysis of the phase transition kinetics and binding energy states of solution processed methylammonium lead iodide (MAPbI3) thin films prepared at ambient conditions and annealed at different elevated temperatures. It is the processing temperature and environmental conditions that predominantly control the crystal structure and surface morphology of MAPbI3 thin films. The structural transformation from tetragonal to cubic occurs at 60 °C with a 30 minute annealing time while the 10 minute annealed films posses a tetragonal crystal structure. The transformed phase is greatly intact even at the higher annealing temperature of 150 °C and after a time of 2 hours. The charge transfer interaction between the Pb 4f and I 3d oxidation states is quantified using XPS