Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Fabrication of cadmium sulfide/p type silicon heterojunction solar cells under 300 °C with more than 10% efficiency Bing Gao a , Yingwen Zhao a , Lun Cai a , Peilin Liu a , Zongcun Liang a,b , Hui Shen a,b, ⁎ a Institute for Solar Energy Systems, Guangdong Provincial Key Laboratory of Photovoltaic Technology, Sun Yat-sen University, Guangzhou 510006, China b Shun De-SYSU Institute for Solar Energy Systems, Shun De 528300, China ARTICLE INFO Keywords: CdS/p-Si heterojunction solar cells Low temperature process Long-term stability ABSTRACT Cadmium sulfide (CdS) film is combined to p-type silicon substrate in order to fabricate heterojunction solar cells. The optimized efficiency with inserting MoO 3 layer between cadmium sulfide and silicon reaches 10.64%, with open voltage, short current density and fill factor of 543 mV, 28.75 mA/cm 2 and 68.13% under traditional condition of 300 °C. Finally, the cell’s degradation rate is 5.30% in two months, indicating that this is a stable cell design. 1. Introduction Solar cells are in principle composed of a p-n junction close to the device’s surface. Front strip finger ohmic contact and entire back ohmic contact are usually designed for one-side solar cells (Bullock et al., 2016; De Wolf et al., 2012; Hilali and Nakayashiki, 2006). In conven- tional silicon solar cells, p-n junction is fabricated by diffusion method at 800–900 °C (Polman et al., 2016; Jeffrey, 2014), resulting in a high energy consumption, which is also harmful to wafer quality. In contrast, heterojunction solar cells are appealing due to the low manufacture cost and low temperature coefficient. Silicon heterojunction solar cells (SHJ) stands for high open voltage, low temperature coefficient and small energy budget. This sort of device recently achieved the efficiency record of 26.67% for crystalline silicon solar cells (Kim and Kim, 2015; Yamaguchi et al., 2003; Kinoshita et al., 2011). These excellent per- formances mostly thank to surface passivation by intrinsic a-Si:H. However, the equipment of PECVD (Plasma Enhanced Chemical Vapor Deposition) which is used to fabricate the amorphous silicon film and low temperature silver past are expensive, which leads to the total cost of SHJ cells are still uncompetitive opposed to traditional thermal power generation (Mikio et al., 2014; Kim et al., 2015). Searching for novel heterojunction solar cell design is yet to be a hot issue. Semiconductor compound film/silicon based heterojunction solar cells (other than amorphous silicon film) tend to solve the problems that both the low cost and high efficiency. CdS/p-Si heterojunction solar cells are one of this kind of solar cells. CdS/p-Si heterojunction solar cells were systematically investigated since 1980 (Arya et al., 1982; Coluzza et al., 1980; Swades Ranjan Bera and Satyajit Saha, 2016; Katiyar et al., 2015; Coluzza et al., 1980). Arya group reported an efficiency of 11.3% with a small area of 0.16 cm 2 (Arya et al., 1982). F. J. Garcia et. al published 8.1% efficiency, with larger area of 2 × 2 cm 2 (Garcia et al., 1988). Chuan He and co-workers applied ITO in CdS/p-Si solar cells, but the cells nearly have no efficiency (He et al., 2011). The efficiency of CdS/p-Si heterojunction solar cells with a larger area of 1 × 1 cm 2 in the present work reaches 10.64%. 2. Experimental The fabrication procedure of CdS/p-Si heterojunction solar cells is described as below. Mirror-polished p type (1 0 0) CZ-Si wafer with 1–5 Ω cm resistivity was forward to standard RCA cleaning, followed by loading into a vacuum evaporation system. Cadmium sulfide powder (99.999% purity; Sigma company) was evaporated from the tungsten boat onto the silicon substrate, under temperature of 25 °C and pressure of 1e-3 Pa. The film growth rate is 0.5–3 Å/s and the thickness ranges from 60 nm to 300 nm. Next, aluminum doped zinc oxide (AZO) thin film was prepared by a DC magnetron sputtering, with power density around 4.1 W/cm 2 and substrate temperature of 250 °C. A piece of soda- lime glass employed as the substrate of CdS film was fixed on a parallel carrier to the target surface with the target-substrate distance of 90 mm. The moving speed of the carrier was 3 mm/s during deposition. After that, a stack with silver layer sandwiched by two AZO layers (AZO/Ag/ AZO) film is prepared by co-sputtering silver and AZO targets; Hydrogen is adopted during sputtering in order to obtain AZO:H film. https://doi.org/10.1016/j.solener.2018.06.016 Received 13 April 2018; Received in revised form 17 May 2018; Accepted 4 June 2018 ⁎ Corresponding author at: Institute for Solar Energy Systems, Guangdong Provincial Key Laboratory of Photovoltaic Technology, Sun Yat-sen University, Guangzhou 510006, China. E-mail address: shenhui1956@163.com (H. Shen). Solar Energy 173 (2018) 635–639 0038-092X/ © 2018 Elsevier Ltd. All rights reserved. T