Theoretical Study of Electronic Properties of Organic Photovoltaic Materials ERIKA IVONNE LO ´ PEZ-MARTI ´ NEZ, 1 LUZ MARI ´ A RODRI ´ GUEZ-VALDEZ, 2 NORMA FLORES-HOLGUI ´ N, 1 ALFREDO MA ´ RQUEZ-LUCERO, 1 DANIEL GLOSSMAN-MITNIK 1 1 NANOCOSMOS Group and PRINATEC, Centro de Investigacio´n en Materiales Avanzados S.C. Chihuahua, Chih C.P. 31109, Me´xico 2 Facultad de Ciencias Quı´micas, Universidad Auto´noma de Chihuahua, Chihuahua, Chih C.P. 31000, Me´xico Received 9 October 2007; Revised 14 August 2008; Accepted 15 August 2008 DOI 10.1002/jcc.21126 Published online 22 October 2008 in Wiley InterScience (www.interscience.wiley.com). Abstract: It has been proved that fullerene derivatives, in which an oligophenylenevinylene (OPV) group is attached to C 60 , present an interesting photophysical phenomenon and can be incorporated into photovoltaic cells. In these systems, the OPV acts as electron donor upon excitation, and then fullerene absorbs photoexcited electrons. These new organic semiconductor materials offer the prospect of lower manufacturing costs and they present several advantages: easy fabrication, large area, flexible and light weight devices when compared with inorganic counter parts. In the present theoretical study, oligomeric chains of p-phenylenevinylene (n-PPV, n 5 3–8 units) and C 60 - OPV hybrids have been studied by density functional theory (DFT). Electronic properties such as electronic absorp- tion and emission spectra were calculated in order to determinate how the increment of spectroscopic units affects their electronic behavior. These properties were carried out with time dependent-density functional theory (TD-DFT) and ZINDO semiempirical method. The theoretical calculations of the structural properties of n-PPV and fullerene- OPV hybrids were obtained using PBE1PBE/6-31G and ONIOM two-layered version, respectively. All calculations were done with Gaussian 03W program package. q 2008 Wiley Periodicals, Inc. J Comput Chem 30: 1027–1037, 2009 Key words: DFT; time dependent-DFT; ZINDO method; electronic transference; donor–acceptor system; electronic spectrum Introduction Although common materials used in photovoltaic devices are inorganic, in the past three decades, there has been an important effort to develop photovoltaic cells. 1 The field of organic elec- tronic is rapidly expanding because of the promise of inexpen- sive material and easy fabrication accompanied by the wide va- riety of functionality of organic materials. 2–4 This research area began with the application of small molecules like pigments, and now, with the development of the semiconducting polymers, these materials have been incorporated to the semiconductors devices with important improvement. 5 A conjugated polymer consists of a large number of segments, called chromophores, which absorb and emit light. These are very promising active materials, which combine the optoelectronic properties of semiconductors with the mechanical properties and processing advantages of plastics when compared with its inorganic coun- ter-parts. 6 It has been proved experimentally, in the case of thio- phen and phenyl-vinyl oligomers, and theoretically, in the case of phenyl-vinylen oligomers, that chains with more than 5–8 repeated units bear all the essential electronic properties of the infinite polymer chains that concern absorption and emission of light. 5,7,8 Other functional materials are fullerenes. As a new form of carbon, fullerene (C 60 ) is an excellent electron acceptor. Sariciftci et al. 9 discovered the photoinduced electron transfer from semiconducting polymers and oligomers to fullerenes, with interesting and unique photophysical properties in those compo- sites. In recent times, a new concept of devices was proposed, i.e., an interpenetrating blends of donors (p-hole conductor poly- mer) and acceptors (electron acceptor molecule C 60 n-type), ‘‘sandwiched’’ between two asymmetric contacts (two metals with different work functions). 10,11 In such bulk heterojunctions organic solar cells, two different organic materials possessing electron donor and electron acceptor properties, respectively, are Contract/grant sponsor: Consejo Nacional de Ciencia y Tecnologı ´a (CONACYT) Correspondence to: L. M. Rodrı ´guez-Valdez; e-mail: luz.rodriguez@ cimav.edu.mx q 2008 Wiley Periodicals, Inc.