PNNL

Abstract

Cadmium sulfide (CdS) thin films are commonly used as buffer layers in thin film solar cells. Continuous solution deposition of CdS on Fluorine-doped tin oxide coated glass substrates is demonstrated using Microchannel-Assisted Chemical Solution Deposition (MASDTM) that uses a flow system consisting of a microscale T- mixer and a novel adjustable residence time microchannel heat exchanger. CdS reaction involves a multistage mechanism with competing undesirable homogeneous reaction and desirable heterogeneous reaction. A microchannel heat exchanger with an adjustable residence time unit has been developed to optimize the reaction residence time. Optimization of CdS reaction solution residence time facilitates improved control of CdS reaction by minimizing homogeneous reaction and subsequently improving key parameters for process scale up such as yield and selectivity. The present study indicates that a residence time range of 13-20s at a solution temperature of 90oC and deposition time of 3 minutes yields ~40 nm thick CdS film. The CdS film thickness was characterized by UV-Vis spectroscopy and the film morphology was characterized by SEM-EDS, TEM, and XRD techniques.