Solution-grown CdS layers for polycrystalline-thin-film solar cells

Abstract

Solution growth of CdS layers was investigated for use as heterojunction partner in CuInSe, and CdTe polycrystallinethin-film solar cells. Morphological and optical properties improved significantly when buffer solution was used. Cadmium acetate was found to be preferable as cadmium ion source as compared to cadmium chloride. Optimum conditions for slow ion-by-ion growth on Sn0,:F coated glass substrates of conformal CdS 500-2600 A thick layers with direct bandgap of -2.40 eV were cadmium salt concentration Q in the range 0.001-0.003 M, tluourea concentration 5 x Q, buffer solution concentration 20 x Q, pH in the range of 9.0-9.5, deposition temperature of 80-85" C and deposition time of 13-30 min. Heterogeneous growth on the substrate was found to depend critically on the availability of nucleation sites.

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

“…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.…”

“…Mainly for the economical reason, from this point on we will refer to it as economical formulation-although this can be further enhanced-whose specifications are depicted in Table 3. These specifications can be changed-usually a variation in the Cd 2+ concentration is done-but it is necessary to take into account that the deposition conditions, like the pH of the On the other hand, although different authors have included in their reports studies in which the reaction temperature is varied [12,15,[20][21][22][23][24]27,28,34,35,54,73,[77][78][79][80][81]84,85,87,89,90,, there is no report about the energy consumption of the equipment that keeps constant the temperature of the water bath at a selected value. For this purpose, we measured the energy consumption during the first minutes when a temperature of 30˚C, 50˚C, and 70˚C is achieved, starting from a water bath at 25˚C.…”