Electrical and optical characterization of SiO x N y and SiO 2 dielectric layers and rear surface passivation by using SiO 2 /SiO x N y stack layers with screen printed local Al-BSF for c-Si solar cells Nagarajan Balaji a , Huong Thi Thanh Nguyen b , Cheolmin Park a , Minkyu Ju b , Jayapal Raja b , Somenath Chatterjee c , R. Jeyakumar d , Junsin Yi b, * a Department of Energy Science, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do 440-746, Republic of Korea b College of Information and Communication Engineering, Sungkyunkwan University, 300 Cheoncheon -dong, Jangan-gu, Suwon, Gyeonggi-do 440-746, Republic of Korea c Department of Electronics and Communication Engineering, Sikkim Manipal Institute of Technology, Sikkim Manipal University, Sikkim 737102, India d Physics of Energy Harvesting Division, CSIR-National Physical Laboratory, New Delhi 110 012, India article info Article history: Received 14 May 2017 Received in revised form 22 August 2017 Accepted 7 October 2017 Available online xxx Keywords: Rear surface passivation c-Si solar cell Refractive index Interface trap density Surface recombination velocity abstract In c-Si solar cells, surface recombination velocity increases as the wafer thickness decreases due to an increase in surface to volume ratio. For high efficiency, in addition to low surface recombination velocity at the rear side, a high internal reflection from the rear surface is also required. The SiO x N y film with low absorbance can act as rear surface reflector. In this study, industrially feasible SiO 2 /SiO x N y stack for rear surface passivation and screen printed local aluminium back surface field were used in the cell structure. A 3 nm thick oxide layer has resulted in low fixed oxide charge density of 1.58  10 11 cm 2 without parasitic shunting. The oxide layer capped with SiO x N y layer led to surface recombination velocity of 155 cm/s after firing. Using single layer (SiO 2 ) rear passivation, an efficiency of 18.13% has been obtained with V oc of 625 mV, J sc of 36.4 mA/cm 2 and fill factor of 78.7%. By using double layer (SiO 2 /SiO x N y stack) passivation at the rear side, an efficiency of 18.59% has been achieved with V oc of 632 mV, J sc of 37.6 mA/ cm 2 , and fill factor of 78.3%. An improved cell performance was obtained with SiO 2 /SiO x N y rear stack passivation and local BSF. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Over the last decade, crystalline silicon (c-Si) wafer based solar cells with screen printed front and rear contacts has been domi- nating the commercial photovoltaic industry [1] owing to its simplicity and reduced manufacturing cost (Fig. 1). Another aspect to reduce the cost is to use thinner wafers (<200 mm). However, high recombination (300e600 cm/s) [2] as well as low surface reflectance (<65%) at the rear side of the cell limits the usage of thin wafers in front contact and back contact solar cells. These limita- tions have been controlled by using passivated emitter and rear cell (PERC) architecture [3e7]. Usually, to improve internal reflection significantly [8,9], dielectric layer (for example SiO 2 ) with low refractive index (1.45) is placed at the rear side between the metal contact and c-Si absorber followed by screen printed aluminum (Al) paste to form local p þ -region (known as local Al back surface field or local Al-BSF) within the dielectric openings. As compared to full area Al-BSF [10], local Al-BSF (Fig. 2) reduces the recombination and improves surface reflectance at the rear side. The maximum gain in cell efficiency can be achieved by using localized back contacts (Fig. 2) and dielectric rear surface passivation technology through the reduction of surface recombination accomplished by dielectric films [11e 13]. Various dielectric layers such as thermally grown SiO 2 [14], plasma-enhanced chemical vapour deposited (PECVD) SiN x [15,16], SiC x [17], a-Si [18] or SiO x [19] and atomic layer deposited (ALD)- Al 2 O 3 layer [20] have been used for rear side passivation. In the case of PERC solar cells with screen printed Al dots, during high tem- perature firing process, severe degradation was observed in the thermal oxide (105 nm thick SiO 2 ) passivation layer [7]. This limi- tation was overcome by using SiN x layer at the rear side (instead of SiO 2 ) as they could withstand high temperature firing process [21]. * Corresponding author. E-mail address: junsin@skku.edu (J. Yi). Contents lists available at ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap https://doi.org/10.1016/j.cap.2017.10.004 1567-1739/© 2017 Elsevier B.V. All rights reserved. Current Applied Physics xxx (2017) 1e7 Please cite this article in press as: N. Balaji, et al., Electrical and optical characterization of SiO x N y and SiO 2 dielectric layers and rear surface passivation by using SiO 2 /SiO x N y stack layers with screen printed local Al-BSF for c-Si solar cells, Current Applied Physics (2017), https:// doi.org/10.1016/j.cap.2017.10.004