Photothermal conversion of the single-source precursor of copper sulfide

by Abhisakh Sarma (DESY)




One of the most straightforward and most direct methods of harvesting visible light is to convert the incident visible radiation into heat (called photothermal conversion).  One of the key components in photothermal conversion systems is its optical absorption and its light to heat conversion efficiency.  With our present-day of understanding, an efficient way to harvest the visible light is to utilize the high absorbance property of selected material nanocrystals in the visible or infrared region. Out of existing nanostructure materials, copper chalcogenide nanoparticles have received increased attention as a well suited photothermal agent due to their low cost,  easy preparation, and high phto thermal conversion efficiency. In recent years, copper sulfide nanocrystals (NCs) have emerged as promising candidates for new photothermal agents due to their strong near-infrared (NIR) light absorption, high photostability.

For the fabrication of copper sulfide nanoparticles with varying, tailor-made morphologies, different synthesis techniques have been used. Among these, synthetic routes based on dry single-source precursors for copper and sulfur are of particular interest because they are cost-effective, employ relatively low temperatures (80 to 200 °C), and produce high quality uniform nanocrystals. Hence, this low-temperature synthesis of copper sulfide from single-source precursors is particularly relevant e.g. during its incorporation and layer processing in flexible thin-film solar cells.

Copper thiourea complexes (CTCs) are well-known single source precursors for copper sulfide nanocrystals. Out of different existing CTC complexes, we worked with the copper thiourea chloride hemihydrate [Cu(tu)]Cl·½H2O, which entirely transformed into copper sulfide once it is heated to 180 °C.  We observed that even though the material fully converts to copper sulfide when it is heated to 180 °C, the initiation of copper sulfide formation could be observed starting at 110 °C (a very small fraction).  The photothermal conversion properties of the tiny fraction generated copper sulfide can be utilized to convert the CTC complex fully to copper sulfide.

Here we will report  that the photothermal conversion of the copper thiourea complex (CTC) to copper sulfide