The dissociation of photogenerated excitons and the subsequent spatial separation of the charges are of crucial importance to the design of efficient donor-acceptor heterojunction solar cells. While huge progress has been made in understanding charge generation at all-organic junctions, the process in hybrid organic:inorganic systems has barely been addressed. Here, we explore the influence of energetic driving force and local crystallinity on the efficiency of charge pair generation at hybrid organic:inorganic semiconductor heterojunctions. We use X-ray diffraction, photoluminescence quenching, transient absorption spectroscopy, photovoltaic device and electroluminescence measurements to demonstrate that the dissociation of photogenerated polaron pairs at hybrid heterojunctions is assisted by the presence of crystalline electron acceptor domains. We propose that such domains encourage delocalization of the geminate pair state. The present findings suggest that the requirement for a large driving energy for charge separation is relaxed when a more crystalline electron acceptor is used.
Bibliographical noteFunding Information:
We acknowledge financial support from the Engineering and Physical Science Research Council (EPSRC) through the Supergen (EP/G031088/1) and UK-India (EP/H040218/2) programmes; SAH and JN acknowledge support from the Royal Society through award of a University Research Fellowship (SAH) and an Industry Fellowship (JN). TK acknowledges support via an Imperial College Junior Research Fellowship.
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