Chemical bath deposition of thin film CdSe layers for use in Se alloyed CdTe solar cells

Abstract

Chemical bath deposition (CBD) was used as a method to deposit CdSe thin films for use in CdTe solar cells. Solution parameters such as precursor stoichiometry, concentration and deposition time, were varied to assess the impact on the morphology of the CdSe films deposited on FTO coated glass. The solution precursors were cadmium acetate and sodium selenosulphite with NH3 used as a complexant to control the release of ions into the solution. It was seen that particle size, surface coverage and thickness were successfully controlled. CdSe films were grown with a band gap of ~1.74 eV and were made into full devices with CdTe. A ternary compound of CdTe1-xSex formed with a band gap of ~1.40 eV, which was shown in an improved EQE in the IR, as well as an improved Jsc. The best device, with an efficiency of 12.3% was produced from a 280 nm thick film with a surface coverage of 59% and grain size of ~600 nm. An increased response at longer wavelengths due to the lowered band gap resulted in a high JSC value of 28.2 mA cm -2 suggesting efficient intermixing of the CdSe into the CdTe1-xSex layer.

Comparison of Cadmium Selenide Thin Films Deposited by Chemical Bath and Pulsed DC Sputtering for use in Cadmium Telluride Devices

“…The chemical bath deposition followed a method previously reported [8] and was optimized to increase the deposition rate. 4 mmol of cadmium acetate, 8 mmol of sodiumselenosulphite and 10 ml of ammonium hydroxide were added to 275 ml of de-ionized water.…”

“…Sponsorship provided by the EPSRC SuperSolar Network lower bandgap allows a greater portion of the solar spectrum to be utilized which effectively raises the short circuit current density (J sc ). In our previous work chemical bath deposition (CBD) of the CdSe layer has been shown to produce CST devices with good initial efficiencies [8] however the rate is very slow with films of 280 nm deposited in 4 hours. Pulsed DC magnetron sputtering offers a way of giving uniform thin films at a much faster rate with better control over the process.…”