Enhancing charge photogeneration and performance of in situ prepared polymer/nanocrystal hybrid solar cells by improved precursor design

Andrew J. MacLachlan^a, Saif A. Haque^a, Thomas Rath^a, Gregor Trimmel^b

^aDepartment of Chemistry and Centre for Plastic Electronics, Imperial College London, South Kensington Campus, London, United Kingdom

^bGraz University of Technology, Institute for Chemistry and Technology of Materials (ICTM), NAWI, Stremayrgasse, 9, Graz, Austria

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Thomas Rath, 127
Publication date: 5th February 2015

Organic-inorganic bulk heterojunction hybrid solar cells based on conjugated polymers and inorganic semiconducting nanocrystals are an exciting solar cell technology as they combine beneficial properties of organic and inorganic semiconductors. Thus, they can take advantage of the high absorption coefficients and easy processability of organic materials as well as the superior electronic properties of inorganic semiconductors. Polymer/nanocrystal hybrid solar cells can be prepared by blending a conjugated polymer with semiconducting nanocrystals stabilized by a capping agent. Besides the advantage that nanocrystals with well-defined sizes and shapes can be used, the main drawback of this approach is that the capping ligands remain at least partly in the absorber layers, where they act as impurity and thus limit the efficient charge separation and transport in the final device. Therefore, we have focused our work on the in situ preparation of nanocrystals directly in the conjugated polymer film leading to ligand-free hybrid interfaces. Using metal xanthates as precursors, hybrid solar cells based on various metal sulfides and conjugated polymers have already been studied.^[1-4] A key issue to further develop in situ prepared hybrid solar cells is an improved control of materials synthesis, in particular, a good control over nanomorphology formation of polymer and nanocrystals in the absorber layer, which critically influences charge separation and also charge transport. Our latest results reveal that the absorber layer nanomorphologies can be optimized via careful design of the precursor materials.^[5] The data obtained from a comprehensive study based on P3HT/CdS nanocrystal hybrid layers acting as a model material system disclose distinct influences of the alkyl moiety of the metal xanthates on the absorber layer nanomorphology. The formation of the nanomorphology during the in situ synthesis of the nanocrystals is thoroughly investigated on the nanometer scale by time resolved grazing incidence small and wide angle X-ray scattering using synchrotron radiation. Furthermore, charge photogeneration in the prepared absorber layers is probed by transient absorption spectroscopy and also the influences on the characteristic solar cell parameters are discussed. The findings of this study will provide a valuable tool for further research in the field of hybrid photovoltaics and, in particular, the further optimization of polymer/nanocrystal hybrid solar cells based on non-toxic material combinations including Sb₂S₃, Bi₂S₃ or CuInS₂ nanocrystals.

[1] Rath, T.; Trimmel, G. In Situ Syntheses of Semiconducting Nanoparticles in Conjugated Polymer Matrices and their Application in Photovoltaics. Hybrid Mater. 2014, 1, 15-36. [2] Dowland, S. A.; Lutz, T.; Ward, A.; King, S. P.; Sudlow, A.; Hill, M. S.; Molloy, K. C.; Haque, S. A. Direct Growth of Metal Sulfide Nanoparticle Networks in Solid-State Polymer Films for Hybrid Inorganic–Organic Solar Cells. Adv. Mater. 2011, 23, 2739-2744. [3] Rath, T.; Edler, M.; Haas, W.; Fischereder, A.; Moscher, S.; Schenk, A.; Trattnig, R.; Sezen, M.; Mauthner, G.; Pein, A.; Meischler, D.; Bartl, K.; Saf, R.; Bansal, N.; Haque, S. A.; Hofer, F.; List, E. J. W.; Trimmel, G. A Direct Route Towards Polymer/Copper Indium Sulfide Nanocomposite Solar Cells. Adv. Energy Mater. 2011, 1, 1046-1050. [4] Bansal, N.; O'Mahony, F. T. F.; Lutz, T.; Haque, S. A. Solution Processed Polymer–Inorganic Semiconductor Solar Cells Employing Sb2S3 as a Light Harvesting and Electron Transporting Material. Adv. Energy Mater. 2013, 3, 986-990. [5] MacLachlan, A. J.; Rath, T.; Cappel, U. B.; Dowland, S. A.; Amenitsch, H.; Knall, A.-C.; Buchmaier, C.; Trimmel, G.; Nelson, J.; Haque, S. A. Polymer/Nanocrystal Hybrid Solar Cells: Influence of Molecular Precursor Design on Film Nanomorphology, Charge Generation and Device Performance. Adv. Funct. Mater. 2015, 25, 409-420.

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