Solution Processing of Chalcogenide Semiconductors via Dimensional Reduction

Abstract

The quest to develop thin‐film solution processing approaches that offer low‐cost and preferably low‐temperature deposition, while simultaneously providing quality semiconductor characteristics, has become an important thrust within the materials community. While inorganic compounds offer the potential for outstanding electronic properties relative to organic systems, the very nature of these materials rendering them good electronic materials—namely strong covalent bonding—also leads to poor solubility. This review presents a “dimensional reduction” approach to improving the solubility of metal chalcogenide semiconductors, which generally involves breaking the extended framework up into discrete metal chalcogenide anions separated by small and volatile cationic species. The resulting soluble precursor may be solution‐processed into thin‐film form and thermally decomposed to yield the desired semiconductor. Several applications of this principle to the solution deposition of high‐performance active layers for transistors (channel mobility >10 cm2 V−1 s−1), solar cells (power conversion efficiency of as high as 12%), and fundamental materials study will be presented using hydrazine as the deposition solvent.

Composition-matched molecular “solders” for semiconductors

“…The pharmacodynamic properties of clinically used ART derivatives [artesunate, artemether, and dihydroartemisinin (DHA)] can reduce the biomass of drug-sensitive parasites by four orders of magnitude every 48 hours (3), corresponding to a single cycle of asexual bloodstage P. falciparum development. The short half-life (typically <1 hour) of ART derivatives in plasma necessitates the use of longer-lasting partner drugs that can eliminate residual parasites once the ART component has dropped to subtherapeutic concentrations (4). The use of ACTs in expanded malaria control and elimination programs has yielded notable successes in recent years, contributing to an estimated 30% reduction in global mortality rates in the past decade (5).…”

Direct Liquid Coating of Chalcopyrite Light‐Absorbing Layers for Photovoltaic Devices

“…While oxide coatings are often treated in air, in order to eliminate carbon contamination, [77][78][79] air-sensitive samples are handled in inert atmosphere. [80][81][82] The final high temperature heat treatment (350-600°C) always requires controlled atmosphere, often with the addition of chalcogen vapor or hydrogen chalcogenide. This final anneal can be preceded by reduction treatments (especially when oxygen is present in the film) and is a critical processing step, defining the properties of the absorber.…”

“…Hydrazine, N 2 H 4 , is another possibility as a solvent. [80][81][82] In many respects, hydrazine is an ideal solvent, since it is strongly reducing and can therefore stabilize the formation of metal chalcogenide anions in solution. It is both small and volatile and also tends not to coordinate strongly.…”

“…This must be taken into account during the subsequent processing steps, as incomplete elimination may lead to severely deteriorated electronic properties or at least impeded grain growth. Some of the described methods, especially the ones based on hydrazine solutions, [80][81][82] aim for exclusion of these impurity elements in the preparation step.…”

“…Physical and chemical properties can be selected to achieve dissolution of desired materials, including pure chalcogenide compounds. [80][81][82][83] While organic solvents rarely introduce oxygen contamination, residual carbon upon pyrolysis may remain in the layers, especially when strong coordination with the metal is present. Hydrazine, N 2 H 4 , is another possibility as a solvent.…”