Al 2 O 3 /Ag/Al 2 O 3 passivating and conducting stacks for crystalline silicon solar cells Shenghao Li a , Yi Dan a , Jixiang Zhou a , Hui Shen a,b, ⁎ a Institute for Solar Energy Systems, Sun Yat-Sen University, 5th floor, C block, School of Engineering, 132 Wai Huan Dong Road, Higher Education Mega Center, Guangzhou, Guangdong 510006, China b Shun De-SYSU Institute for Solar Energy Systems, Shun De 528300, China abstract article info Article history: Received 13 November 2015 Received in revised form 10 June 2016 Accepted 2 July 2016 Available online 02 July 2016 The purpose of this work is to investigate the passivating and conducting layers of crystalline silicon solar cells. The Al 2 O 3 /Ag/Al 2 O 3 stack was chosen because of the free carrier injection effect of this structure. A resistivity as low as 2.81 × 10 -5 Ω cm was achieved with a 16 nm Ag interlayer. The current-voltage measurements indicate that the current density increases with the increasing thickness of the Ag layers. The passivation properties of the stacks were examined by effective minority carrier lifetime measurements. The annealing process was applied to study the thermal stability of the thin film stacks. The best sample yielded an effective surface recombination ve- locity of approximately 50 cm/s and a resistivity of approximately 3.0 × 10 -5 Ω cm. Moreover, the fixed charges of the investigated structures varied according to the thickness of the Ag layers. The experimental results dem- onstrated the promising potential of Al 2 O 3 /Ag/Al 2 O 3 stacks as passivating and conducting layers for crystalline silicon solar cells. © 2016 Published by Elsevier B.V. Keywords: Passivation Surface recombination Minority carrier lifetime Resistivity Al 2 O 3 /Ag/Al 2 O 3 Oxide metal oxide structures Fixed charge 1. Introduction Surface passivation is a critical aspect in the fabrication of crystalline silicon solar cells. For example, passivated emitter and rear cells (PERC) achieve high efficiencies because of the application of rear surface pas- sivation [1]. However, to date, most of the passivation layers are formed of dielectric materials such as silicon dioxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), and silicon nitride (SiN x ). The insulating passivation layers on the surface of the silicon solar cell must be pierced through to enable the transport of the electrons. This is a subtle and complex procedure, and it must be carefully controlled to prevent damage to the silicon sur- face. Ag pastes with glass frits are commonly used on the front surface to fire through the surface passivation layers. Laser ablation is usually employed on the rear surface [2,3] to open the rear surface dielectric layers. In both cases, it is difficult to eliminate the detrimental effects on the silicon surface. Additionally, the direct contact between the sili- con and the metal electrode suffers from the high recombination loss [4,5]. To solve this problem, recent research efforts focus on ultrathin pas- sivation layers [6–9]. The current is tunneled through the dielectric layers by the quantum effect. However, the tunneling rate depends strongly on the thickness of the dielectric layers. In general, a thickness b 3 nm is required to enable good electron transport [7]. However, for passivation layers with a thickness equal to 3 nm, obtaining excellent surface passivation is difficult due to the insufficient thickness. One promising passivated contacts approach is the TOPCon (Tunnel Oxide Passivated Contact) which contains ultrathin tunnel oxide and doped poly-crystalline Si layers. Low contact resistances and low effec- tive surface recombination velocity (SRV) were achieved [10–14] using this method. However, the silicon wafer has to endure high temperature annealing (over 900 °C) during the fabrication. The goal of this work is to fabricate passivating and conducting layers (PCL) that realize both passivation and conduction on the silicon surface. We propose the oxide/metal/oxide (OMO) structure that has been widely researched for improving the conductivity in the transpar- ent conducting oxides (TCO) field. Various oxide materials have been studied, including indium-tin-oxide (ITO) [15–17], zinc oxide (ZnO) [18–23], molybdenum trioxide (MoO 3 ) [24–26] and tungsten trioxide (WO 3 ) [27–29]. This paper explores the Al 2 O 3 /Ag/Al 2 O 3 passivation layers with different thicknesses of Ag layers. The resistivity and SRV of the Al 2 O 3 /Ag/Al 2 O 3 stacks are discussed. Capacitance-voltage (C-V) measurements were performed to investigate the fixed oxide charge of the thin film stacks. The results demonstrate the promising potential of the Al 2 O 3 /Ag/Al 2 O 3 configuration as the PCLs for the crystalline silicon solar cells. Thin Solid Films 615 (2016) 56–62 ⁎ Corresponding author at: Institute for Solar Energy Systems, Sun Yat-Sen University, 5th floor, C block, School of Engineering, 132 Wai Huan Dong Road, Higher Education Mega Center, Guangzhou, Guangdong 510006, China. E-mail address: shenhui1956@163.com (H. Shen). http://dx.doi.org/10.1016/j.tsf.2016.07.002 0040-6090/© 2016 Published by Elsevier B.V. Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf