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Bimolecular recombination in a low bandgap polymer: PCBM blend solar cell with a high dielectric constant

journal contribution
posted on 2024-11-16, 10:04 authored by Guanran Zhang, Tracey Clarke, Attila MozerAttila Mozer
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 x 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.

Funding

Next generation excitonic solar cells using advanced charge generation concepts: setting the new efficiency benchmark

Australian Research Council

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History

Citation

Zhang, G., Clarke, T. M. & Mozer, A. J. (2016). Bimolecular recombination in a low bandgap polymer: PCBM blend solar cell with a high dielectric constant. The Journal of Physical Chemistry C: Energy Conversion and Storage, Optical and Electronic Devices, Interfaces, Nanomaterials, and Hard Matter, 120 (13), 7033-7043.

Journal title

Journal of Physical Chemistry C

Volume

120

Issue

13

Pagination

7033-7043

Language

English

RIS ID

107064

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