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MOCVD of SnSx thin films for solar cell application Andrew J. Clayton, Stuart J. C. Irvine, Vincent Barrioz, Alessia Masciullo Centre for Solar Energy Research, Glyndŵr University, Ffordd William Morgan St. Asaph Business Park, Denbighshire, LL17 0JD, U.K. ABSTRACT An inline metal organic chemical vapor deposition system was used to deposit tin sulfide at temperatures >500 °C. Tetramethyltin was used as the tin source and diethyldisulfide as the sulfur source. An overhead injector configuration was used delivering both precursors directly over the substrate. The tin and sulfur precursors were premixed before injection to improve chemical reaction in the gas phase. Growth temperatures 500 – 540 °C were employed producing films with approximate 1:1 stoichiometry of Sn and S detected by energy dispersive x-ray spectroscopy. X-ray diffraction showed there to be mixed phases with Sn2S3 present with SnS. INTRODUCTION Solar cells incorporating a tin sulfide (SnS) absorber have to date only achieved certified photovoltaic (PV) efficiencies up to 4.4% [1], whereas copper zinc tin sulfide/selenide (CZTS/Se) has reached a cell efficiency of 12.6% [2]. However, secondary phase formation can readily occur in the quaternary structure leading to reduced photovoltaic performance of the solar cell [3]. There may be a number of reasons for low PV cell efficiency for SnS-based solar cell devices, including small grain size leading to a high density of grain boundaries that act as recombination centers [1, 4] and unsuitable chemical band offset [1, 5, 6] between the typical ntype CdS layer and p-type SnS. Earlier work [4, 7] towards producing SnS-based PV cells used CdS as the n-type layer contributing to the p-n junction. However, CdS is considered [1, 5, 6] unsuitable as the n-type buffer with SnS as the p-type absorber due to the chemical band offset. Other n-type materials such as SnS2 [8] and Zn(O,S) [1, 5] have been investigated for creating better band alignment with SnS for improved PV performances. SnS2 offers a more simple solution and allows the same source materials to be used, but the Zn(O,S) approach has advantages for band gap engineering [1, 5] by changing the O and S ratio. In many reports [1, 4, 7] the SnS layers are annealed to improve the properties within the PV device. If the SnS films are deposited at high temperature then the post-growth anneal may not be necessary. High growth temperatures have been shown to benefit grain size for as-grown CdTe-based solar cells [9]. The metal organic chemical vapor deposition (MOCVD) process offers a potential route for increasing SnS thin film grain size due to thermally stable high volatile Sn and S precursors allowing for relatively high deposition temperatures to be employed. This paper reports on a scalable MOCVD process to deposit SnS on to boroaluminosilicate glass substrates at temperatures 500 – 540 °C. EXPERIMENT An inline MOCVD system was employed for producing SnS thin films using tetramethyltin (TMT) with diethyldisulfide (Et2S2) as chemical precursors transported