Low defect interface study of intrinsic layer for c-Si surface passivation in a-Si:H/c-Si heterojunction solar cells Sangho Kim a , Vinh Ai Dao b, c , Chonghoon Shin a , Jaehyun Cho b , Youngseok Lee a , Nagarajan Balaji a , Shihyun Ahn b , Youngkuk Kim b , Junsin Yi a, b, ⁎ a Department of Energy Science, Sungkyunkwan University, Suwon, 440-746, Republic of Korea b School of Information and Communication Engineering, Sungkyunkwan University, Suwon, 440-746, Republic of Korea c Faculty of Materials Science, College of Science, Vietnam National University, Hochiminh, Viet Nam abstract article info Available online 27 March 2012 Keywords: Passivation Spectroscopy ellipsometry Heterojunction solar cells Fraction depletion VHF-PECVD High quality hydrogenated intrinsic amorphous silicon [a-Si:H(i)] layer with adequate hydrogen content and lesser void fraction is the key to obtaining good surface passivated crystalline silicon (c-Si), with high open- circuit voltage (V oc ), which will ultimately make the heterojunction with intrinsic thin layer (HIT) solar cell highly efficient. In this study, we performed good surface passivation of a HIT solar cell by depositing a-Si: H(i) layers at different working pressures from 26.7 to 107 Pa by using very high frequency of 60 MHz plasma-enhanced chemical vapor deposition. Based on spectroscopic ellipsometry and gas depletion analysis, we discuss the influence of the working pressure on the deposition mechanism, interface passivation and ul- timately cell efficiency. Highest minority lifetime of about 4 ms was achieved at the highest working pressure of 107 Pa. The decrease in working pressure results in less denser and/or incorporation of epitaxy layer inside the a-Si:H(i) films, and leads to decrease in c-Si surface passivation. The performance of heterojunction solar cell device was improved with the increase of working pressure and the best photo voltage parameters of the device were found to be V oc of 647 mV, short-circuit current density of 32.28 mA/cm 2 and efficiency of 15.57% at working pressure of 107 Pa. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Heterojunction with intrinsic thin-layer (HIT) solar cells, developed by Sanyo Ltd. in 1994, offers low-cost fabrication for high-efficiency solar cells compared to crystalline silicon (c-Si) solar cell with diffused p–n junctions [1]. The world record efficiency of 23% fabricated base on HIT structures, in which stacks of hydrogenated intrinsic amorphous silicon [a-Si:H(i)] and doped a-Si:H layers help to form both the emitter and the back surface field, is also held by Sanyo group [2]. The a-Si:H(i) layers, which have high amorphicity, adequate hydrogen content and low void fraction, enables to suppress surface recombination at the a- Si:H/c-Si heterointerface, to ensures high cell performance [3]. Deposi- tion condition, however, strongly affects the structural and physical properties of the thin a-Si:H(i) layer. Completely amorphous silicon can be obtained at low temperatures (~100 °C), but, it is believed that an ultra-thin layer on c-Si surface is epitaxial. Again, hydrogen dilution is reported to be a key deposition parameter that controls film quality and phase [1]. During deposition, working pressure could also affect the properties of materials deposited by plasma-enhance vapor deposi- tion via silane depletion [4]. For good surface passivation, as well- known, a low order silane radical such as SiH 3 is preferred, which can be obtained by depositing of a-Si:H(i) films at a high working pressure as well as silane depletion. In spite of the effectiveness of the deposition parameter, fewer studies have focused on the optimization of the deposition condition, especially working pressure, for the excellent properties of a-Si:H(i), Thus, the present paper focuses on such an optimization. Moreover, to obtain high performance devices, it is importance to monitor the properties of the a-Si:H(i) layers. This monitoring is usually difficult for heterojunction solar cells, since the thickness of the a-Si:H(i) layer is of the order of nano-scale [3,5]. Owing to the measurement of phase, spectroscopic ellipsometry (SE) is sensitive to subnanometer changes and the precision of measurements is suffi- cient to allow determination of dielectric function information at the shorter wavelengths from few nanolayers [6]. The measured data of the dielectric function of a-Si:H(i) was first simulated by using the tetrahedron model in combination with the Bruggeman effective me- dium approximation. The hydrogen content, crystalline fraction and void fraction of the film were determined. This method also suggests a way to obtain good quality passivation a-Si:H(i) layer with informa- tion of interface property such as film density and included defects in the film. In this paper, the fabrication of heterojunction solar cell with a dif- ferent working pressure during the deposition of a-Si:H(i) layer is Thin Solid Films 521 (2012) 45–49 ⁎ zCorresponding author at: Department of Energy Science, Sungkyunkwan University, Suwon, 440-746, Republic of Korea. Tel.: +82 31 290 7139; fax: +82 31 290 7159. E-mail address: yi@yurim.skku.ac.kr (J. Yi). 0040-6090/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2012.03.074 Contents lists available at SciVerse ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf