Electroactive Ligands for Quantum dot Photovoltaics

Sustainable energy production is a critical challenge faced by mankind currently and one that will persist in the coming decades. Production of electricity from sunlight is a key technology in the global search for a solution to this problem. Current photovoltaic technologies, especially silicon-based photovoltaics, are widely deployed, however concerns remain over the ability of solar to compete with traditional electricity generation in a truly free market. To this end, secondary and tertiary photovoltaic technologies at the forefront of research are focused on low-cost production methods while at the same time reaching and maintaining the high efficiencies currently on the market.

One current exciting approach taken by research is that of quantum dot photovoltaics. By creating nanoparticles out of semiconductor materials, quantum effects cause the band gap to increase and shift relative to their position in the bulk material. This can be harnessed to convert a larger proportion of sunlight into electricity, and to expand the catalog of suitable photovoltaic materials. Quantum dots can be made at low cost, and their small size allows them to be used in printing technologies for low cost, large area device processing. Of paramount importance to this technology is the separation of these quantum dot nanoparticles, aggregation in close proximity causes the particles to interact in such a way as to destroy their quantum properties. To prevent this, large organic ligands are attached to the quantum dots during their synthesis. These large organic ligands are then exchanged for smaller ones during device production, and different ligands can affect the position and size of the band gaps in quantum dots. Currently, the ligands used to ensure a uniform dispersion of the quantum dots do not contribute to the performance of the photovoltaic device beyond separating the quantum dots and modifying their band gaps. In fact, we believe that the insulating layer of ligands hinders the movement of charges within the device by providing large barriers to electron tunneling between the dots, preventing the charge from leaving the device and reducing efficiency. This research aims to improve device efficiency by using ligands that provide a smaller barrier to electron tunneling. We aim to use ligands with conjugated double bonds commonly seen in plastic electronics and organic photovoltaics. This should make it easier for electrons to tunnel out of the dots, improving charge transport within the device and subsequently its efficiency.

EPSRC's research area is Energy