TY  - JOUR
A1  - Li, Tian-yi
A1  - Benduhn, Johannes
A1  - Li, Yue
A1  - Jaiser, Frank
A1  - Spoltore, Donato
A1  - Zeika, Olaf
A1  - Ma, Zaifei
A1  - Neher, Dieter
A1  - Vandewal, Koen
A1  - Leo, Karl
T1  - Boron dipyrromethene (BODIPY) with meso-perfluorinated alkyl substituents as near infrared donors in organic solar cells
JF  - Journal of materials chemistry : A, Materials for energy and sustainability
N2  - Three furan-fused BODIPYs were synthesized with perfluorinated methyl, ethyl and n-propyl groups on the meso-carbon. They were obtained with high yields by reacting the furan-fused 2-carboxylpyrrole in corresponding perfluorinated acid and anhydride. With the increase in perfluorinated alkyl chain length, the molecular packing in the single crystal is influenced, showing increasing stacking distance and decreasing slope angle. All the BODIPYs were characterized as intense absorbers in near infrared region in solid state, peaking at similar to 800 nm with absorption coefficient of over 280 000 cm(-1). Facilitated by high thermal stability, the furan-fused BODIPYs were employed in vacuum-deposited organic solar cells as electron donors. All devices exhibit PCE over 6.0% with the EQE maximum reaching 70% at similar to 790 nm. The chemical modification of the BODIPY donors have certain influence on the active layer morphology, and the highest PCE of 6.4% was obtained with a notably high jsc of 13.6 mA cm(-2). Sensitive EQE and electroluminance studies indicated that the energy losses generated by the formation of a charge transfer state and the radiative recombination at the donor-acceptor interface were comparable in the range of 0.14-0.19 V, while non-radiative recombination energy loss of 0.38 V was the main energy loss route resulting in the moderate V-oc of 0.76 V.
Y1  - 2018
U6  - https://doi.org/10.1039/c8ta06261g
SN  - 2050-7488
SN  - 2050-7496
VL  - 6
IS  - 38
SP  - 18583
EP  - 18591
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Kurpiers, Jona
A1  - Ferron, Thomas
A1  - Roland, Steffen
A1  - Jakoby, Marius
A1  - Thiede, Tobias
A1  - Jaiser, Frank
A1  - Albrecht, Steve
A1  - Janietz, Silvia
A1  - Collins, Brian A.
A1  - Howard, Ian A.
A1  - Neher, Dieter
T1  - Probing the pathways of free charge generation in organic bulk heterojunction solar cells
JF  - Nature Communications
N2  - The fact that organic solar cells perform efficiently despite the low dielectric constant of most photoactive blends initiated a long-standing debate regarding the dominant pathways of free charge formation. Here, we address this issue through the accurate measurement of the activation energy for free charge photogeneration over a wide range of photon energy, using the method of time-delayed collection field. For our prototypical low bandgap polymer:fullerene blends, we find that neither the temperature nor the field dependence of free charge generation depend on the excitation energy, ruling out an appreciable contribution to free charge generation though hot carrier pathways. On the other hand, activation energies are on the order of the room temperature thermal energy for all studied blends. We conclude that charge generation in such devices proceeds through thermalized charge transfer states, and that thermal energy is sufficient to separate most of these states into free charges.
Y1  - 2018
U6  - https://doi.org/10.1038/s41467-018-04386-3
SN  - 2041-1723
VL  - 9
PB  - Nature Publ. Group
CY  - London
ER  -