1 Novel Nanohybrid Structured Regioregular Polyhexylthiophene 2 Blend Films for Photoelectrochemical Energy Applications 3 Manoj K. Ram,* ,‡,§,^ Humberto Gomez, †,||,^ Farah Alvi, ‡ Elias (Lee) Stefanakos, § Yogi Goswami, § and 4 Ashok Kumar †,‡ 5 † Department of Mechanical Engineering, University of South Florida, 4202 East Fowler Avenue, ENB 118, Tampa, Florida 33620, 6 United States 7 ‡ Nanotechnology Research and Education Center, University of South Florida, Tampa, Florida 33620, United States 8 § Clean Energy Research Center, University of South Florida, Tampa, Florida 33620, United States 9 ) Universidad del Norte, KM 5 Via Pto. Colombia, Barranquilla, Colombia 10 b S Supporting Information 27 ’ INTRODUCTION 28 In recent years, photoelectrochemical organic light-emitting 29 diodes, optoelectronics, and solar cell devices based on conju- 30 gated polymers (p-type) and inorganic nanomaterials (n-type) 31 have been studied due to their high electron mobility, chemical 32 and physical stability of inorganic nanoparticles, and flexibility in 33 fabrication of larger cells at low cost. 1,2 The promising photo- 34 conversion efficiencies in photovoltaic systems with PbSe, CdS, 35 CdSe, and nanocrystals in hybrid structures with conjugated 36 polymers in multilayered systems have been studied at large. 3À7 37 Even if a polymerÀnanocrystal system appears promising, use of 38 a toxic precursor (i.e., Cd, Pb, etc.) remains, until today, as a 39 limitation to their development as an alternative to inorganic 40 devices on a large-scale fabrication. In this context, ZnO and 41 TiO 2 nanomaterials, which are nontoxic, offer physical and chemical 42 stability and are promising candidates for hybrid heterojunction 43 photovoltaic cells. 8À10 Recently, reports have been devoted to 44 polymer blends based on TiO 2 nanocrystals because of a strong 45 incompatibility of the nanoparticles with common organic solvents. 46 Use of higher hole mobility polymers, such as poly(3-hexylthiophene), 47 blended with TiO 2 commercial nanocrystals for photovoltaic 48 device applications, has shown external quantum efficiencies up 49 to 15% in an overall AM1.5 solar power conversion system. 11À13 50 More recently, the blends of conjugated polymers and inorganic 51 nanocrystals have offered high electron mobility with improved 52 spectral coverage for energy applications. 14,15 The effective con- 53 duction path for charge transport in conjugated polymer blends 54 with metal oxides or quantum dots still remains a challenge. 16 55 The regioregular polyhexylthiophene (RRPHTh) is one of the 56 most studied materials having a structure similar to hairy-rod 57 polymers and forms semicrystalline films with crystalline do- 58 mains embedded in an amorphous matrix. 17À19 The high degree 59 of crystallinity and strong interchain interactions in RRPHTh 60 would lead to a higher charge mobility since the carriers are no 61 longer confined to a single chain. 20À22 Recently, nanodiamond 62 (NDs) particles have gained worldwide attention due to facile 63 surface functionalization, biocompatibility, quantum information 64 processing, magnetotometry, novel imaging, and IR fluorescence 65 applications and have been shown to enhance the optical and 66 electrochemical properties of conducting polymers. 23 67 In order to fully exploit the advantages of RRPHTh in blend 68 structures, an attempt has been made to blend RRPHTh with Received: June 6, 2011 Revised: September 22, 2011 11 ABSTRACT: The present study shows for the first time the novel photoelectrochemical 12 studies on nanohybrid films fabricated by blending regioregular polyhexylthiophene 13 (RRPHTh) conducting polymer with nanodiamond (ND) nanoparticles. The photoelec- 14 trochemical properties of NDÀ RRPHTh nanohybrid films have been compared by 15 blending RRPHTh with zinc oxide (ZnO) and titanium oxide (TiO 2 ) nanoparticles 16 deposited on indium tin oxide (ITO) coated glass plates, n-type silicon, and gold-coated 17 glass substrates. The NDÀRRPHTh film has revealed more promising morphological and 18 photoelectrochemical properties than RRPHTh, ZnOÀRRPHTh, and TiOÀ-RRPHTh 19 nanohybrid films. The photoelectrochemical study has shown the photoinduced electron 20 transfer in NDÀRRPHTh nanohybrid films where RRPHTh acts as the donor and ND as the 21 acceptor, providing a molecular approach to high-efficiency photoelectrochemical conver- 22 sion properties. The photoelectrochemical properties of NDÀRRPHTh deposited on either 23 n-type silicon or ITO-coated glass plates in an electrolyte containing tetrabutylammonium 24 tetrafluoroborate (TBATFB) is around 8À10 times higher in current density and energy conversion efficiencies compared to 25 RRPHTh, ZnOÀRRPHTh, and TiO 2 ÀRRPHTh nanohybrid films. The Journal of Physical Chemistry C | 3b2 | ver.9 | 12/10/011 | 18:49 | Msc: jp-2011-05297n | TEID: dmadmin | BATID: 00000 | Pages: 8.8 ARTICLE pubs.acs.org/JPCC rXXXX American Chemical Society A dx.doi.org/10.1021/jp205297n | J. Phys. Chem. C XXXX, XXX, 000–000