Journal
ORGANIC ELECTRONICS
Volume 14, Issue 7, Pages 1744-1748Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.orgel.2013.04.015
Keywords
Roll-to-roll gravure; Flexible organic photovoltaics; Spectroscopic ellipsometry; Phase separation; Roll-to-roll drying; Printed P3HT:PCBM
Funding
- National Strategic Reference Framework (NSRF) [09SYN-82-747, 09SYN-42-722]
- EC [REGPOT-286022]
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In order to achieve the cost-efficient scalability of flexible organic photovoltaics (OPVs), the optimization of key factors related to the materials and roll-to-roll (R2R) processes is necessary. The limited drying during the R2R printing process induces a vertical phase separation leading to the formation of a P3HT-rich top region on the photoactive layer which acts as an electron barrier in normal geometry. We show that the increase of R2R drying time and/or post-annealing can enhance the OPV efficiency by the diffusion of PCBM towards the photoactive layer surface forming an electron transport network. It is estimated that the volume fraction of PCBM at the top region of the films triples from about 9% to 30%. In addition, the direct exposure of PEDOT:PSS to air after printing leads to morphological changes that negatively affect the efficiency. Therefore, the protection of PEDOT: PSS from air in combination to the increase of the R2R drying time enables the significant increase of the R2R printed OPVs efficiency to 1%. (C) 2013 Elsevier B.V. All rights reserved.
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