TY  - JOUR
A1  - Alqahtani, Obaid
A1  - Babics, Maxime
A1  - Gorenflot, Julien
A1  - Savikhin, Victoria
A1  - Ferron, Thomas
A1  - Balawi, Ahmed H.
A1  - Paulke, Andreas
A1  - Kan, Zhipeng
A1  - Pope, Michael
A1  - Clulow, Andrew J.
A1  - Wolf, Jannic
A1  - Burn, Paul L.
A1  - Gentle, Ian R.
A1  - Neher, Dieter
A1  - Toney, Michael F.
A1  - Laquai, Frederic
A1  - Beaujuge, Pierre M.
A1  - Collins, Brian A.
T1  - Mixed Domains Enhance Charge Generation and Extraction in Bulk-Heterojunction Solar Cells with Small-Molecule Donors
JF  - Advanced energy materials
N2  - The interplay between nanomorphology and efficiency of polymer-fullerene bulk-heterojunction (BHJ) solar cells has been the subject of intense research, but the generality of these concepts for small-molecule (SM) BHJs remains unclear. Here, the relation between performance; charge generation, recombination, and extraction dynamics; and nanomorphology achievable with two SM donors benzo[1,2-b:4,5-b]dithiophene-pyrido[3,4-b]-pyrazine BDT(PPTh2)(2), namely SM1 and SM2, differing by their side-chains, are examined as a function of solution additive composition. The results show that the additive 1,8-diiodooctane acts as a plasticizer in the blends, increases domain size, and promotes ordering/crystallinity. Surprisingly, the system with high domain purity (SM1) exhibits both poor exciton harvesting and severe charge trapping, alleviated only slightly with increased crystallinity. In contrast, the system consisting of mixed domains and lower crystallinity (SM2) shows both excellent exciton harvesting and low charge recombination losses. Importantly, the onset of large, pure crystallites in the latter (SM2) system reduces efficiency, pointing to possible differences in the ideal morphologies for SM-based BHJ solar cells compared with polymer-fullerene devices. In polymer-based systems, tie chains between pure polymer crystals establish a continuous charge transport network, whereas SM-based active layers may in some cases require mixed domains that enable both aggregation and charge percolation to the electrodes.
KW  - charge transport
KW  - domain purity
KW  - microscopy
KW  - mixed domains
KW  - organic solar cells
KW  - photovoltaic devices
KW  - resonant X-ray scattering
KW  - small molecules
KW  - transient spectroscopy
Y1  - 2018
U6  - https://doi.org/10.1002/aenm.201702941
SN  - 1614-6832
SN  - 1614-6840
VL  - 8
IS  - 19
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Perdigón-Toro, Lorena
A1  - Le Quang Phuong, 
A1  - Eller, Fabian
A1  - Freychet, Guillaume
A1  - Saglamkaya, Elifnaz
A1  - Khan, Jafar
A1  - Wei, Qingya
A1  - Zeiske, Stefan
A1  - Kroh, Daniel
A1  - Wedler, Stefan
A1  - Koehler, Anna
A1  - Armin, Ardalan
A1  - Laquai, Frederic
A1  - Herzig, Eva M.
A1  - Zou, Yingping
A1  - Shoaee, Safa
A1  - Neher, Dieter
T1  - Understanding the role of order in Y-series non-fullerene solar cells to realize high open-circuit voltages
JF  - Advanced energy materials
N2  - Non-fullerene acceptors (NFAs) as used in state-of-the-art organic solar cells feature highly crystalline layers that go along with low energetic disorder. 
Here, the crucial role of energetic disorder in blends of the donor polymer PM6 with two Y-series NFAs, Y6, and N4 is studied. 
By performing temperature-dependent charge transport and recombination studies, a consistent picture of the shape of the density of state distributions for free charges in the two blends is developed, allowing an analytical description of the dependence of the open-circuit voltage V-OC on temperature and illumination intensity. 

Disorder is found to influence the value of the V-OC at room temperature, but also its progression with temperature. Here, the PM6:Y6 blend benefits substantially from its narrower state distributions. 
The analysis also shows that the energy of the equilibrated free charge population is well below the energy of the NFA singlet excitons for both blends and possibly below the energy of the populated charge transfer manifold, indicating a down-hill driving force for free charge formation. 
It is concluded that energetic disorder of charge-separated states has to be considered in the analysis of the photovoltaic properties, even for the more ordered PM6:Y6 blend.
KW  - energetic disorder
KW  - non-fullerene acceptors
KW  - open-circuit voltage
KW  - organic solar cells
Y1  - 2022
U6  - https://doi.org/10.1002/aenm.202103422
SN  - 1614-6832
SN  - 1614-6840
VL  - 12
IS  - 12
PB  - Wiley-VCH
CY  - Weinheim
ER  -