Enhanced organic solar cells efficiency through electronic and electro-optic effects resulting from charge transfers in polymer hole transport blends

Calvyn T. Howells, Khalid Marbou, Haeri Kim, Kwang Jin Lee, Benoît Heinrich, Sang Jun Kim, Aiko Nakao, Tetsua Aoyama, Seiichi Furukawa, Ju Hyung Kim, Eunsun Kim, Fabrice Mathevet, Stéphane Mery, Ifor D.W. Samuel, Amal Al Ghaferi, Marcus S. Dahlem, Masanobu Uchiyama, Sang Youl Kim, Jeong Weon Wu, Jean Charles RibierreChihaya Adachi, Dong Wook Kim, Pascal André

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

We demonstrate that blending fluorinated molecules in PEDOT:PSS hole transport layers (HTL) induces charge transfers which impact on both charge extraction and photogeneration within organic photovoltaic (OPV) devices. OPVs fabricated with modified HTL and two photoactive polymer blends led systematically to power conversion efficiencies (PCE) increases, with PTB7:PC70BM blend exhibiting PCE of ∼8.3%, i.e. ∼15% increase compared to pristine HTL devices. A reduced device-to-device characteristics variations was also noticed when fluorinated additives were used to modify the PEDOT:PSS. Shading lights onto the effect of HTL fluorination, we show that the morphology of the polymer:PCBM blends remains surprisingly unaffected by the fluorinated HTL surface energy but that, instead, the OPVs are impacted not only by the HTL electronic properties (work function, dipole layer, open circuit voltage, charge transfer dynamic) but also by alteration of the complex refractive indices (photogeneration, short circuit current density, external quantum efficiencies, electro-optic modelling). Both mechanisms find their origin in fluorination induced charge transfers. This work points towards fluorination as a promising strategy toward combining both external quantum efficiency modulation and power conversion efficiency enhancement in OPVs. Charge transfers could also be used more broadly to tune the optical constants and electric field distribution, as well as to reduce interfacial charge recombinations within OPVs.

Original languageEnglish
Pages (from-to)4252-4263
Number of pages12
JournalJournal of Materials Chemistry A
Volume4
Issue number11
DOIs
StatePublished - 2016

Bibliographical note

Funding Information:
P. A. thanks the Canon Foundation in Europe for supporting his visits to the RIKEN through a personal Fellowship, and the OSC to access the facilities. K. J. L., H. K., J. H. K., E. S. K., J. W. W., D. W. K. and P. A. were supported by funding of the Ministry of Science, ICT & Future Planning, Korea (201000453, 2015001948, 2014M3A6B3063706). Part of this work has been carried out in the framework of CNRS International Associated Laboratory "Functional nanostructures: morphology, nanoelectronics and ultrafast optics" (LIA NANOFUNC), France. T. A. would like to acknowledge funding from the Japanese Society for the Promotion of Science via a JSPS KAKENHI grant (no. 22350084). J. C. R. and C. A. would like to acknowledge financial support from the Regional Innovation Strategy Support Program - Kumamoto Area on Organic electronics collaboration - Ministry of Education, Culture, Sports, Science and Technology (MEXT). The authors thank Pohang Accelerator Laboratory (PAL) in South Korea for giving us the opportunity to perform the GIWAXS measurements in the frame of the proposal number "2014-1st-9A-015". The authors are grateful to MEST and POSTECH for supporting these experiments, to Drs Tae Joo Shin and Hyungju Ahn for adjustments and assistance, as well as to other staff members from 9A U-SAXS beamline for further assistance.

Publisher Copyright:
© The Royal Society of Chemistry 2016.

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