Nucleation and Growth of Extremely Thin CdSe Films Electrodeposited from Near-Neutral Electrolytes

Abstract

We report on nucleation and growth of CdSe thin films electrodeposited onto F:SnO 2 -coated glass (FTO) under weakly basic pH conditions. Chronoamperometry and electron microscopy reveal that nucleation sites grow three-dimensionally, coalesce, and form a dense film following the Volmer-Weber growth mechanism. Nucleation and growth were studied as a function of bias potential over the range of −0.95 V to −1.15 V. Fitting a two-rate model to current transients at different potentials shows that more negative bias potentials leads to larger nucleation densities and growth rates. Larger nucleation density results in coalescence at smaller thickness and in more uniform thin coatings, which are important for CdSe thin film applications such as extremely thin absorber solar cells.

Dual Role of Sb-Incorporated Buffer Layers for High Efficiency Cuprous Oxide Photocathodic Performance: Remarkably Enhanced Crystallinity and Effective Hole Transport

“…To investigate the effect of the Cu 2 O:Sb seed layer on the electrochemical behavior in the deposition process, the current transients of the Cu 2 O films on the ITO substrates and the Cu 2 O:Sb seed layers were compared, and the results are shown in Figure a and b, respectively. In general, this current density–time transient graph can be functionally separated into three sections: (i) the nucleation step, which is the negative increment of current density by adatom nucleation of Cu 2 O, (ii) the grain growth step, which is the subsequent decrease of the current density after the electroactive area is maximized, and (iii) the planar diffusion step, which is a nonzero steady-state region due to the formation of a continuous two-dimensional film . These steps could be controlled using the electrodeposition parameters and the conductivity of the substrate.…”

“…In general, this current density−time transient graph can be functionally separated into three sections: (i) the nucleation step, which is the negative increment of current density by adatom nucleation of Cu 2 O, (ii) the grain growth step, which is the subsequent decrease of the current density after the electroactive area is maximized, and (iii) the planar diffusion step, which is a nonzero steadystate region due to the formation of a continuous twodimensional film. 20 These steps could be controlled using the electrodeposition parameters and the conductivity of the substrate. In the single-layer Cu 2 O deposition at −0.3 V and pH 11, the nucleation step occurred over a long period of 250 s. The planar diffusion step with saturation current is not typically detected because of the rough surface with a facet structure (Figure 1a).…”

Low‐Temperature Processable High‐Performance Electrochemically Deposited p‐Type Cuprous Oxides Achieved by Incorporating a Small Amount of Antimony

“…The current is maximized until the diffusion zones around all nuclei overlap. After that, the current decreased due to the impingement of growth centers, resulting in a decrease in the effective electrode surface area (region II), followed by a gradual approach to a steady state value by forming a 2D continuous layer (region III) . For the electrochemical analysis, the electrodeposition of cuprous oxide thin films was carried out in an aqueous solution of pH 11 and an applied potential of −0.4 V. Interestingly, the time corresponding to maximum current ( t max ) for the Cu 2 O:Sb is just below 1/4 of that for the u‐Cu 2 O, as shown in Figure , where t max in the Cu 2 O:Sb electrodeposition is around 2 s (point A).…”

Ultrafast Charge Carrier Dynamics in Extremely Thin Absorber (ETA) Solar Cells Consisting of CdSe-Coated ZnO Nanowires

“…CdSe coatings were electrodeposited galvanostatically onto ZnO nanowire arrays at a current density of 1.62 mA cm –2 . This current density was previously reported by our group to give continuous, conformal coatings without codepositing Cd and Se metals . A final charge density of 162 mC cm –2 was used to deposit approximately 30 nm of CdSe on ZnO nanowire arrays that were 1000 nm long with a diameter of 50 nm for standard ETA cells.…”

“…This current density was previously reported by our group to give continuous, conformal coatings without codepositing Cd and Se metals. 37 A final charge density of 162 mC cm −2 was used to deposit approximately 30 nm of CdSe on ZnO nanowire arrays that were 1000 nm long with a diameter of 50 nm for standard ETA cells. The CdSe coating thickness for ETA cells used in TA experiments was 15 nm on ZnO nanowire arrays that were 500 nm long and 50 nm in diameter, controlled with a final charge density of 41 mC cm −2 .…”