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Researchers Find New Electrical Applications of Photo/thermochromic Materials

 

Change of electrical signals along with the external stimuli is highly promising for application on single-molecule switches, wearable electronic skins, sensors, etc. Electron-transfer (ET) type photo/thermochromic materials usually generate stable charge-separation state under the stimulation of light or heat. The change of electron density offers the opportunity to modulate electrical properties of semiconductors.

Recently, the team led by Prof. WANG Mingsheng and Prof. GUO Guocong from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences (CAS), had made new breakthroughs in the exploration of electrical applications of photo/thermochromic materials.

In a study published in J. Am. Chem. Soc., the team reported a photochromic inorganic-organic hybrid semiconductor with high stability to heat, wet, and light. It has a nanoribbon array structure where 1-D semiconducting inorganic nanoribbons covalently bond to 1-D semiconducting organic π-aggregates.

After photoinduced ET, it yields a long-lived charge-separated state with a broad absorption band covering the 200-900 nm region. After coloration, the conductance increased 1800 times and this contrast value represents a record for photoswitchable semiconductors. The photoconductance also increased after coloration, and this is the first example of modifying photoconductance of semiconductors through photoinduced ET.

In a word, this work offers a new design strategy to improve absorption range, conductance, photoconductance, and stability of lead-halide semiconductors, which may help in the exploration of more light absorbers for solar cells.

In another study published in Angew. Chem. In. Ed., the team reported a thermochromic viologen-templated haloplumbate semiconductor with a novel 3D inorganic open framework. A fact is that more than 700 items on organically modified haloplumbates can be found in the CCDC database, but there are only several reported examples of 3D inorganic frameworks.

The compound showed conductance switch in the thermochromic process. The yellow as-prepared crystalline sample turned brown after thermally annealing above 220 oC, with the conductance fell by 84.3%. After re-annealing at low temperature, such as at 150 oC for a certain time, the original color and conductance were restored. XPS and ESR data demonstrated that the thermochromic phenomenon originated from a Br MV2+ ET process and the formation of MV radicals. The dropping of conductance was assigned to the decrease of charge carriers caused by the trapping of electrons by the localized viologen cations.

In a word, this work not only offers a new and effective strategy to modify electrical properties of semiconductors without altering components or structures, but also inspires the development of over-temperature color indicators and circuit overload protectors.

 

 

Schematic representation of the photochromic inorganic-organic hybrid semiconductor. (Image by Prof. GUO’s Group)

 

Contact:

Prof. WANG Mingsheng & Prof. GUO Guocong

Fujian Institute of Research on the Structure of Matter

Chinese Academy of Sciences

Email: mswang@fjirsm.ac.cn; gcguo@fjirsm.ac.cn

 

 


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