Environmentally friendly colloidal quantum dots for high performance solar cells – QDSOC

A photovoltaic (PV) cell is a device that converts sunlight, which is a clean and reliable form of renewable energy, into electricity. The foremost challenge in the PV cell industry is to lower the cost of delivered solar electricity, and this requires the increase of the power conversion efficiencies (PCEs), in addition to reduced fabrication costs. In conventional (bulk) single junction PV cells, photons with energies below the semiconductor bandgap are not harvested while those with higher energies produce hot carriers and, upon cooling down (thermalization), the excess energy gets wasted as heat. Therefore, novel materials with a bandgap tunable to match the spectral distribution of the solar spectrum are crucially needed. Quantum dots (QDs) are nanocrystals exhibiting a tunable bandgap as a result of size and/or composition variation, and have been demonstrated to be of high interest in PV applications. Moreover, QDs-sensitized solar cells (QDSSCs) present promising cost-effective alternatives to conventional silicon semiconductor due to their outstanding properties, such as simplicity in fabrication, possibility to absorb light in wide solar spectrum regions, and theoretical conversion efficiency up to 44%. Over the last 20 years, various small bandgap QDs like PbS or CdTe were successfully used as photosensitizers in PV cells, but the toxicity of the Pb2+ and Cd2+ heavy metal cations are of concern from both human health and environmental standpoints. This toxicity has also severely hampered the industrial development of these PV devices.
This collaborative project aims to develop new QDSSCs using heavy metal-free QDs as absorbing material in the visible and infrared regions for optimal use of the solar spectrum. For that purpose, the French and South African partners will jointly develop new synthetic routes of Ag-In-Zn-Se and CsSnX3-xYx (X, Y = halogen) QDs, respectively, that have demonstrated high potential for PV applications. The interface between Ag-In-Zn-Se or CsSnX3-xYx QDs and the TiO2 photoelectrode will be engineered in Belgium and Morocco from wet and vacuum deposition processes, respectively, and deeply characterized to optimize the exciton dissociation and the charge transfer via the formation of continuous and highly condensed interpenetrating QDs nanochannels into the TiO2 network. Mechanistic studies will allow to investigate the excited state and charge transfer properties of Ag-In-Zn-Se and CsSnX3-xYx, as well as their interaction with TiO2 to boost further the efficiency of QDSSCs. Full solid-state devices will be assembled in Belgium and Morocco and their photoconversion behavior and (opto)electronic properties will be deeply investigated to better understand the relations between the microstructural, light absorption and charge transfer properties of the materials developed. Prototypes of larger scale devices will also be investigated by the Moroccan partner as a proof of concept. Our main goal is to achieve a PCE value above 15%, which would constitute a ground-breaking performance for heavy metals-free PV cells.
All the skills required for an adequate development of the project are present in the four involved teams. This project will enable a strong collaboration between the partners and contribute to the training of young scientists (recruited PhD students and researchers), who will become leaders in this research field in the near future.
The project fully meets EU objectives of finding new materials, better design PV cells to make more efficient solar panels and lower the cost of generating clean and renewable electricity. Results will also enable the development of devices that will allow not only autonomous but also decarbonated production of electricity and thus ensure energy independence, including numerous isolated populations in Africa. This collaborative research will sustain significant progress towards a highly efficient, large scale, low-cost and flexible PV cells solution