Relating open-circuit voltage losses to the active layer morphology and contact selectivity in organic solar cells
Artikel i vetenskaplig tidskrift, 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.


Z. Tang

Linköpings universitet

Donghua University

Jing Wang

Donghua University

A. Melianas

Linköpings universitet

Yang Wu

Xi'an Jiaotong University

Renee Kroon

Chalmers, Kemi och kemiteknik, Tillämpad kemi

Weiwei Li

Chinese Academy of Sciences

W. Ma

Xi'an Jiaotong University

Mats Andersson

Flinders University

Z. F. Ma

Donghua University

Wanzhu Cai

Linköpings universitet

W. Tress

Ecole Polytechnique Federale de Lausanne (EPFL)

O.W. Inganäs

Linköpings universitet

Journal of Materials Chemistry A

20507488 (ISSN) 20507496 (eISSN)

Vol. 6 26 12574-12581


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