Template Engineering of CuBi<sub>2</sub>O<sub>4</sub> Single‐Crystal Thin Film Photocathodes
Jongmin Lee, Hongji Yoon, Kyoung Soon Choi, Seung‐Kyu Kim, Sehun Seo, Jaesun Song, Byeong-Uk Choi, Jiseung Ryu, Sangwoo Ryu, Jihun Oh, Cheolho Jeon, Sanghan Lee
Abstract
Abstract To develop strategies for efficient photo‐electrochemical water‐splitting, it is important to understand the fundamental properties of oxide photoelectrodes by synthesizing and investigating their single‐crystal thin films. However, it is challenging to synthesize high‐quality single‐crystal thin films from copper‐based oxide photoelectrodes due to the occurrence of significant defects such as copper or oxygen vacancies and grains. Here, the CuBi 2 O 4 (CBO) single‐crystal thin film photocathode is achieved using a NiO template layer grown on single‐crystal SrTiO 3 (STO) (001) substrate via pulsed laser deposition. The NiO template layer plays a role as a buffer layer of large lattice mismatch between CBO and STO (001) substrate through domain‐matching epitaxy, and forms a type‐II band alignment with CBO, which prohibits the transfer of photogenerated electrons toward bottom electrode. The photocurrent densities of the CBO single‐crystal thin film photocathode demonstrate −0.4 and −0.7 mA cm −2 at even 0 V RHE with no severe dark current under illumination in a 0.1 m potassium phosphate buffer solution without and with H 2 O 2 as an electron scavenger, respectively. The successful synthesis of high‐quality CBO single‐crystal thin film would be a cornerstone for the in‐depth understanding of the fundamental properties of CBO toward efficient photo‐electrochemical water‐splitting.