Impact of Molecular Organization on Exciton Diffusion in Photosensitive Single-Crystal Halogenated Perylenediimides Charge Transfer Interfaces

authors	Pinto, RM; Gouveia, W; Macoas, EMS; Santos, IC; Raja, S; Baleizao, C; Alves, H
nationality	International
journal	ACS APPLIED MATERIALS & INTERFACES
author keywords	organic semiconductors; single crystals; charge-transfer interfaces; photodetectors; perylenediimides
keywords	FIELD-EFFECT TRANSISTORS; ORGANIC PHOTOVOLTAIC CELLS; SEMICONDUCTOR THIN-FILMS; SOLAR-CELLS; QUANTUM EFFICIENCY; PERFORMANCE; NANOSTRUCTURES; GENERATION; TRANSPORT; SOLIDS
abstract	The efficiency of organic photodetectors and optoelectronic devices is strongly limited by exciton diffusion, in particular for acceptor materials. Although mechanisms for exciton diffusion are well established, their correlation to molecular organization in real systems has received far less attention. In this report, organic single-crystals interfaces were probed with wavelength-dependent photocurrent spectroscopy and their crystal structure resolved using X-ray diffraction. All systems present a dynamic photoresponse, faster than 500 ms, up to 650 nm. A relationship between molecular organization and favorable exciton diffusion in substituted butyl-perylenediimides (PDIB) is established. This is demonstrated by a set of PDIBs with different intra- and interstack distances and short contacts and their impact on photoresponse. Given the short packing distances between PDIs cores along the same stacking direction (3.4-3.7 angstrom), and across parallel stacks (2.5 angstrom), singlet exciton in these PDIBs can follow both Forster and Dexter exciton diffusion, with the Dexter-type mechanism assuming special relevance for interstack exciton diffusion. Yet, the response is maximized in substituted PDIBs, where a 2D percolation network is formed through strong interstack contacts, allowing for PDIBs primary excitons to reach with great efficiency the splitting interface with crystalline rubrene. The importance of short contacts and molecular distances, which is often overlooked as a parameter to consider and optimize when choosing materials for excitonic devices, is emphasized:
publisher	AMER CHEMICAL SOC
issn	1944-8244
year published	2015
volume	7
issue	50
beginning page	27720
ending page	27729
digital object identifier (doi)	10.1021/acsami.5b08523
web of science category	Nanoscience & Nanotechnology; Materials Science, Multidisciplinary
subject category	Science & Technology - Other Topics; Materials Science
unique article identifier	WOS:000367561500020
link	http://pubs.acs.org/doi/abs/10.1021/acsami.5b08523