Byung-Seok Lee

Suppressed Formation of Conductive Phases in One-Pot Electrodeposited CuInSe2 by Tuning Se Concentration in Aqueous Electrolyte

The single-bath electrochemical deposition of CuInSe2 often leads to short-circuit behavior of the resulting solar cells due to the high shunt conductance. In this study, in an attempt to resolve this problem, the influence of the Se precursor concentration (CSe) on electrodeposited CuInSe2 films and solar cell devices is examined in the CSe range of 4.8 to 12.0 mM in selenite-based aqueous solutions containing Cu and In chlorides along with sulfamic acid (H3NSO3) and potassium hydrogen phthalate (C8H5KO4) additives. As CSe increases, the CuInSe2 layers become porous, and the grain growth of the CuInSe2 phase is restricted, while the parasitic shunting problem was markedly alleviated, as unambiguously demonstrated by measurements of the local current distribution. Due to these ambivalent influences, an optimal value of CSe that achieves the best quality of the films for high-efficiency solar cells is identified. Thus, the device prepared with 5.2 mM Se exhibits a power-conversion efficiency exceeding 10% with greatly improved device parameters, such as the shunt conductance and the reverse saturation current. The rationale of the present approach along with the physicochemical origin of its conspicuous impact on the resulting devices is discussed in conjunction with the electro-crystallization mechanism of the CuInSe2 compound.

High-density Cu–In intermetallic nanocrystal layers: towards high-efficiency printable CuInSe2 solar cells

This paper aims to demonstrate the importance of the precursor film density during the development of the microstructure and photovoltaic properties of CuInSe2 (CISe) thin films prepared from nanoparticulate precursors and to provide a simple but effective means to improve the density. In order to improve the packing density of a Cu–In alloy nanocrystalline layer deposited by a doctor-blade method, a mild, wet, ball-milling technique is applied to colloidal ink without the use of organic additives or mechanical pressing. The focused ion beam milled cross-sections clearly show that the relative density of the precursor layers increases with an increase in the milling duration. The CISe thin films obtained by annealing the intermetallic layers with a relative density of 0.78 exhibit extremely low porosity on the well-faceted surface, a thicker top layer with large grains in a typical double-layered structure, a uniform and planar surface morphology, and a thinner MoSe2 layer. The transmission electron microscopy analysis also reveals that the nanocrystals in the bottom layer exist in the chalcopyrite CISe phase, forming a well-connected mesoporous network. As a result, the PV performance of low-bandgap (1.0 eV) CISe solar cells is greatly improved, rendering a power conversion efficiency as high as 9.32%. Changes in the PV parameters induced by the increase in the relative density of the precursor layer are discussed in conjunction with the improved crystalline quality and the consequent improvements in diode characteristics, such as the series resistance, shunt conductance, and recombination current.

Phosphate sorption characteristics of zirconium meso-structure synthesized under different conditions

In this study, the phosphate sorption characteristics of zirconium meso-structures synthesized under different conditions were estimated. X-ray diffraction analysis, phosphate sorption isotherm test and kinetic test were performed for the zirconium meso-structures, synthesized at different inorganics/surfactant molar ratio and with different surfactant (Cx TMA-Br) templates. From the test results, it was found that at the inorganic/surfactant molar ratio of 1/0.50 the meso-pores in the material were most uniformly and clearly formed and thus the sorption capacity and reaction rate of material were maximized. The pore size in meso-structure decreased with the increase in chain length of surfactant template used, and maximum phosphate sorption amount and reaction rate were achieved in the zirconium mesostructure synthesized with the surfactant of dodecyltrimethylammonium bromide (C12 TMA-Br).