title: Correlation between Photovoltaic Performance and Interchain Ordering Induced Delocalization of Electronics States in Conjugated Polymer Blends.
abstract: In this paper we correlate the solar cell performance with bimolecular packing of donor:acceptor bulk heterojunction (BHJ) organic solar cells (OSCs), where interchain ordering of the donor molecule and its influence on morphology, optical properties, and charge carrier dynamics of BHJ solar cells are studied in detail. Solar cells that are fabricated using more ordered defect free 100% regioregular poly(3-hexylthiophene) (DF-P3HT) as the donor polymer show ca. 10% increase in the average power conversion efficiency (PCE) when compared to that of the solar cell fabricated using 92% regioregularity P3HT, referred to as rr-P3HT. EQE and UV-vis absorption spectrum show a clear increase in the 607 nm vibronic shoulder of the DF-P3HT blend suggesting better interchain ordering which was also reflected in the less Urbach energy (Eu) value for this system. The increase in ordering inside the blend has enhanced the hole-mobility which is calculated from the single carrier device J-V characteristics. Electroluminance (EL) studies on the DF-P3HT system showed a red-shifted peak when compared to rr-P3HT-based devices suggesting low CT energy states in DF-P3HT. The morphologies of the blend films are studied using AFM and grazing-incidence wide-angle X-ray scattering (GIWAXS) suggesting increase in the roughness and phase segregation which could enhance the internal scattering of the light inside the device and improvement in the crystallinity along alkyl and π-stacking direction. Hence, higher PCE, lower Eu, red-shifted EL emission, high hole-mobility, and better crystallinity suggest improved interchain ordering has facilitated a more delocalized HOMO state in DF-P3HT-based BHJ solar cells.
authors.affiliation: IITB-Monash Research Academy, IIT Bombay , Mumbai 400076, India.|Department of Physics, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.|Department of Materials Science and Engineering, Monash University , Wellington Road, Clayton, Victoria 3800, Australia.
authors.forename: Naresh
authors.initials: N
authors.lastname: Chandrasekaran
authors.affiliation: Department of Materials Science and Engineering, Monash University , Wellington Road, Clayton, Victoria 3800, Australia.|Australian Synchrotron , 800 Blackburn Road, Clayton, Victoria 3168, Australia.
authors.forename: Eliot
authors.initials: E
authors.lastname: Gann
authors.affiliation: Department of Physics, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.
authors.forename: Nakul
authors.initials: N
authors.lastname: Jain
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.
authors.forename: Anshu
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Centre for Research in Nanotechnology & Science, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.
authors.forename: Sreelekha
authors.initials: S
authors.lastname: Gopinathan
authors.affiliation: Optoelectronics Group, Cavendish Laoratory, University of Cambridge , Cambridge CB3 0HE, United Kingdom.
authors.forename: Aditya
authors.initials: A
authors.lastname: Sadhanala
authors.affiliation: Optoelectronics Group, Cavendish Laoratory, University of Cambridge , Cambridge CB3 0HE, United Kingdom.
authors.forename: Richard H
authors.initials: RH
authors.lastname: Friend
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.
authors.forename: Anil
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Department of Materials Science and Engineering, Monash University , Wellington Road, Clayton, Victoria 3800, Australia.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: McNeill
authors.affiliation: Department of Physics, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.
authors.forename: Dinesh
authors.initials: D
authors.lastname: Kabra
keywords: charge carrier dynamics; defect free P3HT; interchain order; morphology; organic solar cells