Material utilisation when depositing CdTe layers by inline AP-MOCVD

A study was undertaken to assess the efficiency of precursors' usage during deposition of cadmium telluride (CdTe) layers via atmospheric pressure metal organic chemical vapour deposition (AP-MOCVD) for thin film photovoltaic solar cells. Precursors were released from a showerhead assembly normal to the glass substrate 0.7 mm thick (5 x 7.5 cm(2)) being deposited which was kept stationary or moved under the showerhead assembly, with speed of upto 2.25 cm/min. In order to estimate the effective precursor utilisation, the weight deposit (layer) was compared against the theoretical values calculated for ideal molar supply. The layer thickness, composition, morphology, and crystallinity were also measured using profilometry, energy dispersive X-ray (EDX), scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. It is shown that over 40% material utilisation can be achieved depending on the deposition parameters of substrate temperature and speed, partial pressure of precursors and total gas flow. The activation energy derived from an Arrhenius plot of deposition rate equals 49 kJ mol(-1) and is consistent with previous reports of MOCVD CdTe using a horizontal reactor. This confirms that, despite the very different reactor geometry, the alkyl radical homolysis and reaction mechanism applies in the case of the inline injector geometry in the work presented here. These results demonstrate an alternative path to high throughput processing of CdTe thin film solar cells by inline AP-MOCVD. (C) 2012 Elsevier B.V. All rights reserved.