TY  - JOUR
A1  - Nikolis, Vasileios C.
A1  - Benduhn, Johannes
A1  - Holzmueller, Felix
A1  - Piersimoni, Fortunato
A1  - Lau, Matthias
A1  - Zeika, Olaf
A1  - Neher, Dieter
A1  - Koerner, Christian
A1  - Spoltore, Donato
A1  - Vandewal, Koen
T1  - Reducing Voltage Losses in Cascade Organic Solar Cells while Maintaining High External Quantum Efficiencies
JF  - dvanced energy materials
N2  - High photon energy losses limit the open-circuit voltage (V-OC) and power conversion efficiency of organic solar cells (OSCs). In this work, an optimization route is presented which increases the V-OC by reducing the interfacial area between donor (D) and acceptor (A). This optimization route concerns a cascade device architecture in which the introduction of discontinuous interlayers between alpha-sexithiophene (alpha-6T) (D) and chloroboron subnaphthalocyanine (SubNc) (A) increases the V-OC of an alpha-6T/SubNc/SubPc fullerene-free cascade OSC from 0.98 V to 1.16 V. This increase of 0.18 V is attributed solely to the suppression of nonradiative recombination at the D-A interface. By accurately measuring the optical gap (E-opt) and the energy of the charge-transfer state (E-CT) of the studied OSC, a detailed analysis of the overall voltage losses is performed. E-opt - qV(OC) losses of 0.58 eV, which are among the lowest observed for OSCs, are obtained. Most importantly, for the V-OC-optimized devices, the low-energy (700 nm) external quantum efficiency (EQE) peak remains high at 79%, despite a minimal driving force for charge separation of less than 10 meV. This work shows that low-voltage losses can be combined with a high EQE in organic photovoltaic devices.
KW  - energy losses
KW  - nonradiative recombination
KW  - open-circuit voltage
KW  - organic solar cells
KW  - voltage losses
Y1  - 2017
U6  - https://doi.org/10.1002/aenm.201700855
SN  - 1614-6832
SN  - 1614-6840
VL  - 7
SP  - 122
EP  - 136
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Fang, Lijia
A1  - Holzmueller, Felix
A1  - Matulaitis, Tomas
A1  - Baasner, Anne
A1  - Hauenstein, Christoph
A1  - Benduhn, Johannes
A1  - Schwarze, Martin
A1  - Petrich, Annett
A1  - Piersimoni, Fortunato
A1  - Scholz, Reinhard
A1  - Zeika, Olaf
A1  - Koerner, Christian
A1  - Neher, Dieter
A1  - Vandewal, Koen
A1  - Leo, Karl
T1  - Fluorine-containing low-energy-gap organic dyes with low voltage losses for organic solar cells
JF  - Synthetic metals : the journal of electronic polymers and electronic molecular materials
N2  - Fluorine-containing donor molecules TFTF, CNTF and PRTF are designed and isomer selectively synthesized for application in vacuum-deposited organic solar cells. These molecules comprise a donor acceptor molecular architecture incorporating thiophene and benzothiadiazole derivatives as the electron-donating and electron-withdrawing moieties, respectively. As opposed to previously reported materials from this class, PRTF can be purified by vacuum sublimation at moderate to high yields because of its higher volatility and better stabilization due to a stronger intramolecular hydrogen bond, as compared to TFTF and CNTF. The UV-vis absorption spectra of the three donors show an intense broadband absorption between 500 nm and 800 nm with, similar positions of their frontier energy levels. The photophysical properties of the three donor molecules are thoroughly tested and optimized in bulk heterojunction solar cells with C-60 as acceptor. PRTF shows the best performance, yielding power conversion efficiencies of up to 3.8%. Moreover, the voltage loss for the PRTF device due to the non radiative recombination of free charge carriers is exceptionally low (0.26 V) as compared to typical values for organic solar cells (>0.34V). (C) 2016 Published by Elsevier B.V.
KW  - (Z)-isomer
KW  - Donor materials
KW  - CH center dot center dot center dot F hydrogen bonds
KW  - Sublimation with good yield
KW  - Low voltage losses
Y1  - 2016
U6  - https://doi.org/10.1016/j.synthmet.2016.10.025
SN  - 0379-6779
VL  - 222
SP  - 232
EP  - 239
PB  - Elsevier
CY  - Lausanne
ER  -