Photovoltaic Devices based on Colloidal Nanocrystals as Light Harvesters – PvCoNano

- Colloidal synthesis
- Transmission electron microscopy
- UV-Vis absorbance
- Photoluminescence
- FT-IR absorbance

Results 1 : The synthesis set-up is operational.

Results 2 : The initial ligand-exchange experiment is successful

Results 3 : The optical and structural characterizations are operational

The above 2 tasks (Month 0 - 6) will be continued until month 12. A new task (iii) Device fabrication will start during month 7 to 12. We will prepare and purchase all necessary substrates and materials for device fabrications.

Scientific publications are currently under preparation.

In the search for cost-effective solar cells, photovoltaic devices based on solution-processed nanostructured materials including conjugated polymers, small molecules, and colloidal nanocrystals have received much interest over the past decade. Among different material systems, the lead chalcogenide PbSe and PbS nanocrystals are of particular interest due to their excellent photosensitivity in the near-infrared spectrum. Yet the current performance of these nanocrystal solar cells remains poor and carrier recombination is one of the major issues still to be addressed. Methods such as engineering the donor-acceptor interface by molecular modifiers and employing high aspect-ratio nanocrystals have been shown to improve the photovoltaic performance in other hybrid systems but have not been systematically investigated in lead chalcogenide nanocrystal solar cells. Therefore, in this "PVcoNano" project we aim to study the influence of (1) various nanocrystal surface treatments by ligand exchange and (2) different nanocrystal morphologies on the device performance and carrier recombination kinetics in lead chalcogenide nanocrystal solar cells. It can be anticipated that through this study we will gain fundamental understandings on how different surface ligands and nanocrystal morphologies can tune charge transport, charge recombination, and improve the final device performance of PbSe or PbS nanocrystal solar cells. Understanding these aspects will not only lead to improved nanocrystal systems (with optimized ligand choice and beneficial crystal morphologies) for photovoltaic applications but also open further directions in the search for optimized materials eventually leading to the realisation of efficient and inexpensive solar cells.

This 3-year ANR project will be decomposed into four scientific tasks, involving studies of (1) colloidal nanocrystal synthesis, surface ligands, and nanocrystal morphologies; (2) optical and structural characterizations; (3) device fabrication; (4) solar cell performance measurements, and correlation with charge transport and carrier recombination kinetics. To complete these tasks, a team is formed based on four permanent members working at IM2NP (UMR 6242) with complementary backgrounds and two non-permanent members.

Among permanent members, Zhuoying Chen (project responsible), Damien Barakel and Laurent Ottaviani are currently all working in the research group "OPTO-PV". Martiane Cabié is working as a research engineer on material characterization using electron microscopy. Z. Chen (31-year-old, 85%) has a solid and multi-disciplinary research background on colloidal synthesis, material characterization, and optoelectronic devices fabrication and measurements. She will thus direct the synthesis and the device fabrication parts of this project and contribute to optical characterization. D. Barakel (33-year-old, 30%) and L. Ottaviani (40-year-old, 30%) will bring their expertise, respectively, in solar cell performance measurements and in carrier recombination kinetics. They will thus lead the task on device measurements and device physics of this project. Finally, as an expert in electron microscopy applied to material science, M. Cabié (33-year-old, 15%) will complete the structural characterization part of this project.

For non-permanent members, we ask for a 24-month postdoctoral position through this project to work on colloidal nanocrystal solar cells. A PhD thesis has been requested to the "Ecole Centrale - China" 2011 Scholarship and will be co-directed by Z. Chen and L. Escoubas at IM2NP. Half of this PhD thesis will contribute to this ANR project through the characterization of solar cell performance and the study of carrier recombination.
With the addition of the experimental equipments funded through this ANR project, we will have the experimental autonomy required to complete successfully all planned experiments at IM2NP.