Relating open-circuit voltage losses to the active layer morphology and contact selectivity in organic solar cells
Journal article, 2018

We demonstrate that voltage losses due to both radiative and non-radiative recombination of charge carriers are strongly dependent on D/A phase separation. By processing the active layer with various solvent additives, we create distinct morphologies that lead to significantly different device open-circuit voltages (VOC), even though the charge transfer state energy (ECT) of the D/A blend remains rather constant. We find that radiative recombination losses are significantly increased for a finely intermixed morphology, due to the large D/A interface area. This leads to a total recombination loss of ECT - qVOC ≈ 0.7 eV. However, considerably smaller losses (0.5 eV), due to suppressed non-radiative recombination, are possible in solar cells where the D/A materials are organized to only allow for selective charge carrier extraction. Using a drift diffusion model, we show that the origin of the reduced non-radiative recombination losses is related to an effect which has not been considered for 'optimized' solar cells-the suppression of minority carrier diffusion to the 'wrong' contact. Our results suggest that the built-in field is not sufficiently strong even in 'optimized' organic solar cells and that selective carrier extraction is critical for further improvements in VOC.

Author

Z. Tang

Linköping University

Donghua University

Jing Wang

Donghua University

A. Melianas

Linköping University

Yang Wu

Xi'an Jiaotong University

Renee Kroon

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Polymer Technology

Weiwei Li

Chinese Academy of Sciences

W. Ma

Xi'an Jiaotong University

Mats Andersson

Flinders University

Z. F. Ma

Donghua University

Wanzhu Cai

Linköping University

W. Tress

Ecole Polytechnique Federale De Lausanne

O.W. Inganäs

Linköping University

Journal of Materials Chemistry A

20507488 (ISSN) 20507496 (eISSN)

Vol. 6 26 12574-12581

Subject Categories

Physical Chemistry

Analytical Chemistry

Other Physics Topics

DOI

10.1039/c8ta01195h

More information

Latest update

11/8/2019