Carrier Selective Contacts Design for Efficient Photocatalytic Water Reduction

Abstract

2-photon tandem device structures that consist of a wide band gap and narrow band gap photoabsorber can maximize photoelectrolysis efficiency since their I-V characteristics match well with that needed for photoelectrolysis [1]. In the case of the narrow band gap (Eg ) material, recent theoretical work has shown that Si has a suitable Eg for the bottom cell of tandem water splitting device [2]. Since current performance of Si PEC cells lag far behind the theoretical limit [3], the need for a different approach increases. Up to now, tremendous efforts have been made to improve the performance of Si-based photocathodes [4-6]. One approach the solar cells industry uses to increase performance is to use metal-oxide-semiconductor (MOS) carrier-selective contacts due to their efficient carrier transport and low recombination [5,6]. However, very little work has been done studying photocatalytic hydrogen evolution reaction (HER) with the MOS structure. Moreover, there has been no detailed report on energy band level analysis to understand how the carriers can be selectively injected.In this work we demonstrate μc-Si/SiO2/p-Si structure (see Figure 1) to both front and back contacts which provide interface passivation and selective injection of minority and majority carrier to solid/liquid interface and back contact, respectively. A transparent TiO2 is placed above the highly doped μc-Si thin film as a conducting protection layer, and then Pt nanoparticles were drop-casted on the samples for photocatalytic HER in 1M HClO4. Using thin film degenerately doped Si as a metallic layer has been employed in recent state-of-art MOS based PV cells [7], but combination with TiO2 as a conducting protection layer for PEC hydrogen production has not been shown so far. Moreover, the details working principles based on the band energy analysis are outlined to understand how the carriers can be injected selectively and transferred to solid/liquid interface in PEC system.1. B. Seger, I.E. Castelli, P.C.K. Vesborg, K.W. Jacobsen, O. Hansen, I. Chorkendorff, Energy Environ. Sci. 7 (2014) 2397–2413. 2. A.B. Laursen, S. Kegnæs, S. Dahl, I. Chorkendorff, Energy Environ. Sci. 5 (2012) 5577. 3. W. Shockley, H.J. Queisser, J. Appl. Phys. 32 (1961) 510–519. 4. D. Bae, T. Pedersen, B. Seger, M. Malizia, A. Kuznetsov, O. Hansen, I. Chorkendorff, P.C.K. Vesborg, Energy Environ. Sci. 8 (2015) 650–660. 5. D. V Esposito, I. Levin, T.P. Moffat, A.A. Talin, Nat. Mater. 12 (2013) 562–8. 6. A.G. Scheuermann, J.P. Lawrence, K.W. Kemp, T. Ito, A. Walsh, C.E.D. Chidsey, P.K. Hurley, P.C. McIntyre, Nat. Mater. (2015) 1–8. 7. F. Feldmann, M. Simon, M. Bivour, C. Reichel, M. Hermle, S.W. Glunz, Sol. Energy Mater. Sol. Cells. 131 (2014) 100–104. Figure 1