Performance of photodetector heterojunctions varies with carbon nanotube diameter

Junctions between the two different materials, single-wall carbon nanotubes (SWCNTs) and perovskite (CsPbBr₃) quantum dots (QDs); a mechanically stable and easily customized photovoltaic material that creates an electrical current from sunlight when paired with another material, such as SWCNTs; form semiconductor heterojunctions that work exceptionally well as a photodetector.  Recent research suggests that increasing the diameter of SWCNTs in SWCNT/perovskite QD heterojunctions improves the optoelectronic, or ability to convert light to electricity, performance of the heterojunction between the two materials.

 

A team of scientists systematically tested the performance effects of varying diameters of SWCNTs, a single layer of carbon atoms that form a hexagonal lattice rolled into a seamless cylinder, with different band gaps, or the amount of energy required for an electron to conduct electric current, in heterojunction films with perovskite QDs.  Their study indicated that increasing the diameter of SWCNTs improved the responsivity, detectivity and response time of this type of heterojunction film.  This effect may be mediated by the enhanced separation and transport of photogenerated excitons, an energy-carrying, neutrally charged electron that combines with a positive electron hole, in the film.

 

The team published the results of their study in the July 27 issue of the journal Nano Research, published by Tsinghua University Press.  

 

“The alignment between the band gaps of SWCNTs and QDs determines the separation of the photogenerated excitons at the heterogeneous interfaces, while different diameter SWCNTs show different carrier capacity and mobility,” said Huaping Liu, the principal investigator of the study and professor at the Institute of Physics at the Chinese Academy of Sciences in Beijing, China.  “These characteristics determine the photoelectronic performance of SWCNTs/perovskite QDs heterojunction films, making it… important to systematically study the diameter effect of different band gap SWCNTs on the photodetection performance of these films.”

 

The team investigated the differences in photodetector performance for SWCNT diameters between 1.0 and 1.4 nm.  Characteristics of each diameter were assessed by exposing the SWCNT/perovskite QD films to 410 nm light at differing intensities and measuring the current-voltage curves of each film.  This data could then be used to determine the photocurrent, photoresponsivity and detectivity at each nanotube diameter.

 

The band gap of SWCNTs is roughly inversely proportional to the diameter of the nanotube. When SWCNT diameter was increased from 1.0 nm to 1.4 nm, the research team observed an increase in responsivity by about one order of magnitude, a 5-fold increase in detectivity and a 4-fold increase in response speed. The larger-diameter SWCNTs measured in the study improved carrier capacity and mobility to enhance film performance.  

 

“The great improvement in the photoelectric performances in films with larger-diameter SWCNTs is attributed to increasing built-in electric fields at the heterojunction interface of s-SWCNTs semiconducting SWCNTs/QDs…, which drives the separation of hole carriers from photogenerated excitons to s-SWCNTs and rapid transport in SWCNT films,” said Liu.

 

Next-generation photodetectors made from SWCNTs and QDs are necessary to reduce material cost, energy consumption and fragility of these types of detectors in future electronics.  Interestingly, SWCNT monolayer films alone are very inefficient at detecting light, and perovskite QD films are prone to low carrier mobility, responsivity and detectivity.  In contrast, perovskite quantum dot films, when paired with SWCNT monolayers, improve optical absorption as a thin, bilayer film with enhanced responsivity.

 

Results from this study will help other scientists in the design and fabrication of new high-performance photodetectors required for optical communications, wearable technologies and other applications in medicine and artificial intelligence.  Liu’s team plans to utilize these experimental findings specifically in the design of optimized photodetectors for use in highly sensitive artificial vision systems.

 

Other contributors include Jing Lin and Yang Huang from the School of Materials Science and Engineering and Hebei Key Laboratory of Boron Nitride Micro and Nano Materials at Hebei University of Technology in Tianjin, China; Yayang Yu from the School of Materials Science and Engineering and Hebei Key Laboratory of Boron Nitride Micro and Nano Materials at Hebei University of Technology in Tianjin, China and the Beijing National Laboratory for Condensed Matter Physics in the Institute of Physics at the Chinese Academy of Sciences in Beijing, China; Wenke Wang, Xiao Li and Linhai Li from the Beijing National Laboratory for Condensed Matter Physics in the Institute of Physics at the Chinese Academy of Sciences in Beijing, China, the Center of Materials Science and Optoelectronics Engineering and the School of Physical Sciences at the University of Chinese Academy of Sciences in Beijing, China and the Beijing Key Laboratory for Advanced Functional Materials and Structure Research in Beijing, China; Shilong Li from the Beijing National Laboratory for Condensed Matter Physics in the Institute of Physics at the Chinese Academy of Sciences in Beijing, China and the Beijing Key Laboratory for Advanced Functional Materials and Structure Research in Beijing, China; Xiaojun Wei and Weiya Zhou from the Beijing National Laboratory for Condensed Matter Physics in the Institute of Physics at the Chinese Academy of Sciences in Beijing, China, the Center of Materials Science and Optoelectronics Engineering and the School of Physical Sciences at the University of Chinese Academy of Sciences in Beijing, China, the Beijing Key Laboratory for Advanced Functional Materials and Structure Research in Beijing, China and Songshan Lake Materials Laboratory in Guangdong, China

 

This work was supported by the National Key Research and Development Program of China (grant nos. 2020YFA0714700 and 2018YFA0208402), the National Natural Science Foundation of China (grant nos. 51820105002, 51872320, 51472264, 11634014 and 52172060), the Strategic Priority Research Program of the Chinese Academy of Sciences (CAS) (grant no. XDB33030100), the Key Research Program of Frontier Sciences, CAS (grant no. QYZDBSSW-SYS028) and the Youth Innovation Promotion Association of CAS (grant no. 2020005).

 

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About Nano Research 

 

Nano Research is a peer-reviewed, international and interdisciplinary research journal, publishes all aspects of nano science and technology, featured in rapid review and fast publishing, sponsored by Tsinghua University and the Chinese Chemical Society. It offers readers an attractive mix of authoritative and comprehensive reviews and original cutting-edge research papers. After 15 years of development, it has become one of the most influential academic journals in the nano field. In 2023 InCites Journal Citation Reports, Nano Research has an Impact Factor of 9.9, the total cites reached 35645, ranking first in China's international academic journals, and the number of highly cited papers reached 194, ranked among the top 1.8% of 8769 academic journals.

 

About Tsinghua University Press

 

Established in 1980, belonging to Tsinghua University, Tsinghua University Press (TUP) is a leading comprehensive higher education and professional publisher in China. Committed to building a top-level global cultural brand, after 42 years of development, TUP has established an outstanding managerial system and enterprise structure, and delivered multimedia and multi-dimensional publications covering books, audio, video, electronic products, journals and digital publications. In addition, TUP actively carries out its strategic transformation from educational publishing to content development and service for teaching & learning and was named First-class National Publisher for achieving remarkable results.

 

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