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Bimolecular Recombination in a Low Bandgap Polymer:PCBM Blend Solar Cell with a High Dielectric Constant

Zhang, G; Clarke, TM; Mozer, AJ; (2016) Bimolecular Recombination in a Low Bandgap Polymer:PCBM Blend Solar Cell with a High Dielectric Constant. The Journal of Physical Chemistry C , 120 (13) pp. 7033-7043. 10.1021/acs.jpcc.6b01169. Green open access

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Abstract

The strength of dielectric screening is one of the most intriguing yet least studied contributing factors to the operation and performance limit of organic solar cell devices. Increasing the dielectric constant of semiconducting polymers may close the performance gap between inorganic and organic solar cell devices. Here, a dielectric constant of 16.7 is reported for a DPP-based low bandgap polymer DT-PDPP2T-TT and 7 for its 1:3 blend with [60]PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) using frequency and voltage dependent capacitance and charge extraction by linearly increasing voltage (CELIV) techniques. The charge mobility within the blend device (1.8 × 10–3 cm2 V–1 s–1) is found to be among the highest reported by CELIV. Bimolecular recombination and charge carrier lifetime in efficient photovoltaic devices are measured and compared to poly(3-hexylthiophene) (P3HT):PCBM (1:1 w/w) and poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT):PCBM (1:2 w/w) devices. When normalized to mobility, the bimolecular recombination coefficient in DT-PDPP2T-TT:PCBM is a factor of 2 lower than in P3HT:PCBM and an order of magnitude lower than in PCPDTBT:PCBM. The recombination mechanism is found to be close to diffusion-controlled Langevin recombination. The reduced recombination is explained by a smaller Coulomb capture radius, which, together with higher charge mobility, leads to efficient charge extraction in photovoltaic devices with large active layer thicknesses approaching 300 nm.

Type: Article
Title: Bimolecular Recombination in a Low Bandgap Polymer:PCBM Blend Solar Cell with a High Dielectric Constant
Open access status: An open access version is available from UCL Discovery
DOI: 10.1021/acs.jpcc.6b01169
Publisher version: http://dx.doi.org/10.1021/acs.jpcc.6b01169
Language: English
Additional information: Copyright © 2016 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in the Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see: http://dx.doi.org/10.1021/acs.jpcc.6b01169.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/1493455
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