Mechanism of Chemical Bath Deposition of Cadmium Sulfide Thin Films in the Ammonia‐Thiourea System: In Situ Kinetic Study and Modelization

Abstract

The mechanism of chemical bath deposition of cadmium sulfide thin films from the ammonia‐thiourea system is studied in situ by means of quartz crystal microbalance technique (QCM). The influence of reaction parameters (concentration of reactants, pH, anions, temperature, stirring rate) is determined. The growth is thermally activated with an activation energy of about 85 kJ/mol, which probably corresponds to a chemical step related to the decomposition of thiourea. The results are well interpreted by assuming an atom‐by‐atom growth mechanism. A model is presented, which fits most of the experimental results quantitatively. It involves two or three rate‐limiting surface steps, the formation of normalCdS taking place via a surface complex between thiourea and cadmium hydroxide. Analytical expressions are given, allowing prediction of the rate under various conditions in this system.

The Zn(S,O,OH)/ZnMgO buffer in thin film Cu(In,Ga)(S,Se)2‐based solar cells part I: Fast chemical bath deposition of Zn(S,O,OH) buffer layers for industrial application on Co‐evaporated Cu(In,Ga)Se2 and electrodeposited CuIn(S,Se)2 solar cells

“…This value is higher than that of Zn(S,O,OH) deposited in the classical conditions (14Á1 kcal mol À1 ) 11 , but remains lower than that of CdS buffer layers (20 kcal mol À1 ). 12,13 However, these values indicate that the process is controlled by chemical surface reactions.…”

Development of thin‐film Cu(In,Ga)Se2 and CdTe solar cells

“…Physical vapor deposition (PVD)-grown CdS layers yield lowerefficiency cells, as thin layers grown by PVD do not show uniform coverage of CIGS and are ineffective in chemically engineering the interface properties. For a comprehensive review on CBD-deposited CdS see Ortega-Borges and Lincot 31 and Hodes. 32 The recent trend in buffer layers is to substitute CdS with 'Cd-free' wide-bandgap semiconductors and to replace the CBD technique with in-line-compatible processes.…”

Detailed Analysis of Five Aspects Addressed to Minimize Costs and Waste in the Chemical Bath Deposition of CdS Films Using the Cd<i>B</i>–<i>A</i>C<sub>6</sub>H<sub>5</sub>O<sub>7</sub>–<i>A</i>OH–(NH<sub>2</sub>)<sub>2</sub>CS System

“…Third, as the amount of CdCl 2 was increased, maintaining constant the immersion time, the log(T -1 ) values also increased. According with that discussed with Equation (2), this is directly related to the increase in thin film d. This increase in the growth rate by increasing the Cd 2+ ions amount is widely supported by the literature [56,60,[77][78][79][80][81][82][83][84][85][86]. Fourth, as reported by Ochoa-Landín et al [60], there is a slight difference between the films deposited in a reaction solution containing pH 10 borate buffer, compared with those deposited in the absence of the buffer.…”

“…Therefore, this small difference in the log(T -1 ) spectra due to a slight decrease in the d-according to Equation (2)-of the films deposited in the presence of the pH 10 buffer, for each immersion time and CdCl 2 concentration, is definitely an effect of the addition of the buffer. One parameter that has not been considered up to this point, and a very important one that also affects the growth rate of the CdS thin films and that could explain the foregoing is the pH of the reaction solutions, whose effect on the growth rate of CdS thin films-or in the precipitation rate of CdS-has been noted by several authors [54,[78][79][80][81][87][88][89].…”

“…However, several authors have reported explicitly or implicitly that the lower the reaction temperature the lower the thin film growth rate [12,15,20,21,23,28,34,35,54,[77][78][79][80][81]84,87,90,[103][104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121]. Thus, without delving into the cases in which homogeneous precipitation is favored, which limits the maximum d-a limit which was directly reported [12,15,21] or simply evident in the results reported [115,118,120] by some authors-the use of low temperatures lengthens the time required to achieve a thin film with determined d compared to the time required at higher temperatures.…”