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The Impact of Device Polarity on the Performance of Polymer–Fullerene Solar Cells
Author(s) -
Li Mengmeng,
Li Junyu,
Di Carlo Rasi Dario,
Colberts Fallon J. M.,
Wang Junke,
Heintges Gaël H. L.,
Lin Baojun,
Li Weiwei,
Ma Wei,
Wienk Martijn M.,
Janssen René A. J.
Publication year - 2018
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201800550
Subject(s) - materials science , polymer , fullerene , polarity (international relations) , polymer solar cell , energy conversion efficiency , solubility , absorption (acoustics) , chemical engineering , organic solar cell , conjugated system , optoelectronics , organic chemistry , composite material , chemistry , biochemistry , engineering , cell
Diketopyrrolopyrrole (DPP)‐conjugated polymers are a versatile class of semiconductors for application in organic solar cells because of their tunable optoelectronic properties. A record power conversion efficiency (PCE) of 9.4% was recently achieved for DPP polymers, but further improvements are required to reach true efficiency limits. Using five DPP polymers with different chemical structures and molecular weights, the device performance of polymer:fullerene solar cells is systematically optimized by considering device polarity, morphology, and light absorption. The polymer solubility is found to have a significant effect on the optimal device polarity. Soluble polymers show a 10–25% increase in PCE in inverted device configurations, while the device performance is independent of device polarity for less soluble DPP derivatives. The difference seems related to the polymer to fullerene weight ratio at the ZnO interface in inverted devices, which is higher for more soluble DPP polymers. Optimization of the nature of the cosolvent to narrow the fibril width of polymers in the blends toward the exciton diffusion length enhances charge generation. Additionally, the use of a retroreflective foil increases absorption of light. Combined, the effects afford a PCE of 9.6%, among the highest for DPP‐based polymer solar cells.