Aug 9, 2012
Mild post-deposition treatments benefit colloidal nanocrystal solar cells
The combination of tunable and broadband absorption and low-cost solution-processing methods have motivated numerous studies on photovoltaic devices made using colloidal nanocrystals (NCs) such as nanorods, hyperbranched structures and tetrapods. Despite all of the advantages, the integration of such materials in photovoltaic devices is challenging because colloidal NCs typically possess electrically insulating ligand shells that must be modified or removed to convert nanocrystalline solids from insulators to conductors.
In a recent study, researchers at the National Nanotechnology Laboratory (NNL)-CNR Istituto di Nanoscienze have examined the use of dilute carboxylic acid solutions on heterostructured CdSe@CdTe tetrapods to promote more effective inter-particle charge transfer and improve the photovoltaic performance of tetrapod-based solar cells.
Treatments with acetic and trifluoroacetic acids on CdSe@CdTe tetrapod solids led to a doubled photovoltaic performance when compared with the standard pyridine exchange procedure.
Through a complete characterization of the treated NC solids (FTIR spectroscopy, AFM inspection and transport measurements) the team showed that the improved photovoltaic performance can be attributed to a complete removal of the insulating organic ligand from the NC surface, which results in better electronic coupling, and optimizes the morphology of the material.
Suits flexible substrates
Post-deposition treatment with carboxylic acids represents an effective low-temperature method to electronically couple CdSe@CdTe-shaped tetrapods for photovoltaic applications. This relatively gentle technique improves charge transport across multiple tetrapods to create pathways for carriers, without disrupting the chemical structure of the NCs and other components of the device.
According to the team, the method is fully compatible with plastic and flexible polymeric device technology.
Full details can be found in the journal Nanotechnology.
About the author
The study was conducted at the National Nanotechnology Laboratory of CNR-Istituto di Nanoscienze. Rosanna Mastria is a graduate student at Università del Salento under the supervision of Dr Aurora Rizzo, who is a CNR-Nanoscienze researcher. The team’s focus is to study novel approaches and systems for the integration of colloidal nanocrystals and polymer materials in hybrid, inorganic and organic photovoltaics. Prof. Giuseppe Gigli is head of the organic optoelectronic device and hybrid/organic photovoltaic divisions.