Piezoelectric-enhanced P-N Junctions in Photoelectrochemical Systems

Photoelectrochemical (PEC) water splitting is a potentially feasible strategy for converting solar energy to green hydrogen. However, current PEC systems suffer from relatively low charge separation efficiency and sluggish water oxidation reactions, which prevent them from meeting the needs of practical applications. The main bottleneck like in achieving effective charge spatial separation, which is crucial for achieving efficient solar-to-hydrogen conversion.

Heterojunction engineering is one of the most promising methods for spatial charge separation, yet the carrier separation efficiency of heterojunction remains limited due to energy band matching or interfacial and structural compatibility between different semiconductors. Meanwhile, the construction of p-n homojunction by finely controlling dopants or defect in semiconductors has been proven to be feasible, but the phenomenon that neutralizes the interfacial electric field through the rapid accumulation of carriers during the transfer process is largely negligible.

To that end, a team of researchers from the School of Chemical Engineering and Technology at Tianjin University designed a unique n-TiO₂/BaTiO₃/p-TiO₂ heterojunction which couples with piezoelectric effect and p-n junctions to overcome the charge separation and transfer limitation of p-n junction.

“In our designed heterojunction, the ferroelectric BaTiO₃ layer is between n-TiO₂ with oxygen vacancies and p-TiO₂ with titanium vacancies,” shares Minhua Ai, lead author of the study published in the KeAi journal Green Energy & Environment. “Consequently, the TBT3 achieves a prominent photocurrent density which is 2.4- and 1.5-times higher than TiO₂ and TiO₂–BaTiO₃ heterojunction, respectively.”

Notably, driven by mechanical deformation, a stable polarized electric field formed in ferroelectric BaTiO3 can further regulate built-in electric fields based on comprehensive characterizations of charge carrier behaviors in such a multi-heterojunction. And n-TiO₂/BaTiO₃/p-TiO₂ heterojunction achieves piezoelectric-enhanced PEC performance (2.84 times higher than TiO₂ at 1.23 V vs. RHE).

“Based on the coupling with piezoelectric effect and p-n junctions, our work provides a piezoelectric polarization strategy for modulating the built-in electric field of heterojunction for charge separation enhancement,” adds senior and corresponding author Lun Pan.

Contact author name, affiliation, email address:  Lun Pan, Key Laboratory for Green Chemical Technology of the Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China. E-mail address: panlun76@tju.edu.cn (L. Pan).

Conflict of interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Founder: The authors appreciate the support from the National Natural Science Foundation of China (22222808, 21978200, 22161142002), the Joint Research Programs of the National Natural Science Foundation of China, and the Pakistan Science Foundation (PSF-NSFC-IV/Phy/P-PU(31)), and the Haihe Laboratory of Sustainable Chemical Transformations for financial support.

See the article: M. Ai et al., Piezoelectric-enhanced n-TiO₂/BaTiO₃/p-TiO₂ heterojunction for highly efficient photoelectrocatalysis, Green Energy & Environment. https://doi.org/10.1016/j.gee.2023.12.001