An effective strategy of constructing a multi-junction structure by integrating a heterojunction and a homojunction to promote the charge separation and transfer efficiency of WO3

Adequate light absorption and effective charge separation and transfer are deemed to be the contributing factors to achieve high photoelectrochemical (PEC) water splitting on photoanodes. Herein, in this work, a Mo-WO3/Fe-WO3 homojunction was fabricated firstly by coating Fe doped WO3 (Fe-WO3) on Mo doped WO3 (Mo-WO3) via a two-step hydrothermal method, and then Bi2S3 nanoparticles (NPs) were further introduced onto the surface of Mo-WO3/Fe-WO3 to construct a multi-junction structure. In this Mo-WO3/Fe-WO3/Bi2S3 photoanode, the Bi2S3 NPs as the primary light absorber improve the light utilization efficiency. Moreover, the Fe-WO3/Bi2S3 heterojunction is formed due to their well-matched bands, which could facilitate charge separation and transfer; meanwhile, the internal built-in electric field at the interface of the Mo-WO3/Fe-WO3 homojunction would hinder the recombination of electron–hole pairs. Notably, the homojunction can further promote carrier transfer because of its unique property of eliminating the lattice mismatch. As expected, the Mo-WO3/Fe-WO3/Bi2S3 photoanode yields a significantly enhanced photocurrent of 2.55 mA cm−2 at 1.23 V vs. RHE, which is 8.23 times that of the WO3 photoanode. Thus, constructing a multi-junction structure with a ladder staggered alignment by integrating a homojunction and a heterojunction is believed to be an effective strategy to improve the PEC performance of WO3 photoanodes.