International Journal of Scientific Engineering and Technology (ISSN : 2277-1581) www.ijset.com, Volume No.1, Issue No.4, pg : 111-116 01 Oct. 2012 Page 111 Plasma Enhanced Chemical Vapor Deposited (Pecvd) Silicon-Rich-Nitride Thin Films For Improving Silicon Solar Cells Efficiency A. Kumar 1 , W.R. Taube 2 , R. Sarvanan 3 , P.B. Agarwal 4 , P. Kothari 5 , D. Kumar 6 1,2,3,4,5 Sensors and Nanotechnology Group, CSIR-Central Electronics Engineering Research Institute (CEERI), Pilani-333031, India 6 Electronics Science Department, Kurukshetra University, Kurukshetra – 136119, India * Corresponding author: akumar1758@yahoo.co.in Abstract Silicon-rich-nitride (SRN) films were deposited by plasma enhanced chemical vapour deposition (PECVD) by changing the silane and ammonia flow rates. These films were thermally annealed for precipitation of silicon nanocrystals. Measurements of refractive indices and FTIR absorption spectra of these films indicated increase in the silicon content. Thermally annealed SRN films exhibited photoluminescence in visible region indicating their potential as down-conversion layer for efficiency improvement in solar cells. A significant relative improvement in conversion efficiency using SiO x /SRN layers in solar cells has been reported in our earlier work. In this paper, we present detailed synthesis process, characterization and analysis of SiN films. Characterization results and solar cell measurements indicate that the observed photoluminescence at 577nm in visible range in selected films along is responsible for improvement in conversion efficiency through down-conversion of high energy solar photons. Keywords: Silicon-rich-nitride, PECVD, Silicon- nanostructures, Down-conversion, Silicon solar cells, Photoluminescence. Introduction PECVD hydrogenated silicon nitride (SiN x :H) thin films have attracted great attention in silicon solar cell manufacturing due to their excellent passivation and anti- reflection properties [1,2]. Silicon nitride films can be deposited by low-pressure-chemical-vapor-deposition (LPCVD) or plasma enhanced chemical vapour deposition (PECVD) techniques. PECVD is well suited for large area solar cell fabrication due to lower deposition temperature. Properties of SiN x :H films can be controlled by varying the process parameters namely, flow rate of silane and ammonia gases, deposition temperature and RF power [3]. In recent years, extensive efforts have been made to improve conversion efficiency of silicon solar cells by employing nanostructures and nanotechnologies [4-6]. In one such approach, nanostructures convert higher energy photons into lower energy photons which are absorbed more efficiently by silicon solar cell [7]. Another proposed mechanism for efficiency enhancement is the generation of multiple excitons in quantum dots by high energy photons (> 2 E g ) [8]. Improvement in open circuit voltage (V OC ) and short circuit current (I SC ) of silicon solar cells have been reported by coating a film of spin-on- glass containing silicon-nanoparticles (SiNP) [9], and silicon nanoparticles’ suspension in organic solvent [10]. But, these approaches were not very effective in improving the performance of solar cells, because these films were applied to the cell after fabrication. An effective approach would be the integration of silicon nanoparticles within the solar cell structure. This integration could be done as silicon-rich-oxide (SRO) or silicon-rich-nitride (SRN) films during fabrication process, these films on thermal annealing result in precipitation of silicon nanocrystals [11]. Recently, integratiing silicon nanocrystals in SRO film on crystalline silicon solar cells has shown improvement in internal quantum efficiency (IQE) for high energy photons, but a reduction in overall power conversion efficiency [12]. SRN is a better material system than SRO, due to lower energy barrier between silicon and silicon-nitride compared with silicon and silicon-oxide and requirement of lower annealing temperature [4, 13]. Also, PECVD silicon nitride films provide good surface passivation. Silicon nanocrystals embedded in dielectric matrix are potential materials for next generation silicon solar cells such as tandem, up/downconversion, and multiple exciton generation [14]. The short term objective of these R & D efforts is to improve the efficiency of silicon solar cells with minimum deviation in the existing technology. This has been the motivation of our study on integrating silicon nanocrystals embedded in PECVD SiN x matrix in the solar cell structure for enhancing the conversion efficiency. Recently, we reported efficiency enhancement in crystalline silicon solar cell with optimized anti-reflection coating (ARC) films embedded with silicon nanocrystals in SiN x matrix by PECVD[15]. In this paper, we present process development of photoluminescent SRN films by PECVD technique, their characterization and analysis. SRN films with favourable composition and properties for application in solar cells efficiency improvement were integrated in solar cells. Methodology: Hydrogenated silicon nitride (SiN x :H) nitride films were deposited on silicon and quartz substrates by PECVD technique using Oxford Instruments TM Plasma Lab equipment. RF (13.56 MHz) was used to create plasma in parallel-plate configuration. Silane and ammonia were used as precursors for silicon and nitorgen. In the present study only the gas flow rates were varied during deposition while other parameters