The room-temperature structure of lysozyme is determined using 40000 individual diffraction patterns from micro-crystals flowing in liquid suspension across a synchrotron microfocus beamline.
Organic photovoltaic (OPV) cells using BTR:PC71BM show promising power conversion efficiency of >28% under 1000 lux generating 78.2 μW cm−2, outperforming Si based PV cells and comparable to GaAs PV cells. This result suggests that OPV cells have excellent potential for indoor applications.
Nonfullerene acceptors (NFAs) dominate organic photovoltaic (OPV) research due to their promising efficiencies and stabilities. However, there is very little investigation into the molecular processes of degradation, which is critical to guiding design of novel NFAs for long‐lived, commercially viable OPVs. Here, the important role of molecular structure and conformation in NFA photostability in air is investigated by comparing structurally similar but conformationally different promising NFAs: planar O‐IDTBR and nonplanar O‐IDFBR. A three‐phase degradation process is identified: i) initial photoinduced conformational change (i.e., torsion about the core–benzothiadiazole dihedral), induced by noncovalent interactions with environmental molecules, ii) followed by photo‐oxidation and fragmentation, leading to chromophore bleaching and degradation product formation, and iii) finally complete chromophore bleaching. Initial conformational change is a critical prerequisite for further degradation, providing fundamental understanding of the relative stability of IDTBR and IDFBR, where the already twisted IDFBR is more prone to degradation. When blended with the donor polymer poly(3‐hexylthiophene), both NFAs exhibit improved photostability while the photostability of the polymer itself is significantly reduced by the more miscible twisted NFA. The findings elucidate the important role of NFA molecular structure in photostability of OPV systems, and provide vital insights into molecular design rules for intrinsically photostable NFAs.
With
the emergence of nonfullerene electron acceptors resulting
in further breakthroughs in the performance of organic solar cells,
there is now an urgent need to understand their degradation mechanisms
in order to improve their intrinsic stability through better material
design. In this study, we present quantitative evidence for a common
root cause of light-induced degradation of polymer:nonfullerene and
polymer:fullerene organic solar cells in air, namely, a fast photo-oxidation
process of the photoactive materials mediated by the formation of
superoxide radical ions, whose yield is found to be strongly controlled
by the lowest unoccupied molecular orbital (LUMO) levels of the electron
acceptors used. Our results elucidate the general relevance of this
degradation mechanism to both polymer:fullerene and polymer:nonfullerene
blends and highlight the necessity of designing electron acceptor
materials with sufficient electron affinities to overcome this challenge,
thereby paving the way toward achieving long-term solar cell stability
with minimal device encapsulation.
The photochemistry and stability of fullerene films is found to be strongly dependent upon film nanomorphology. In particular, PCBM blend films, dispersed with polystyrene, are found to be more susceptible to photobleaching in air than the more aggregated neat films. This enhanced photobleaching correlated with increased oxygen quenching of PCBM triplet states and the appearance of a carbonyl FTIR absorption band indicative of fullerene oxidation, suggesting PCBM photo-oxidation is primarily due to triplet-mediated singlet oxygen generation. PCBM films were observed to undergo photo-oxidation in air for even modest (≤40 min) irradiation times, degrading electron mobility substantially, indicative of electron trap formation. This conclusion is supported by observation of red shifts in photo- and electro-luminescence with photo-oxidation, shown to be in agreement with time-dependent density functional theory calculations of defect generation. These results provide important implications on the environmental stability of PCBM-based films and devices.
The
use of solution processes to fabricate perovskite solar cells
(PSCs) represents a winning strategy to reduce capital expenditure,
increase the throughput, and allow for process flexibility needed
to adapt PVs to new applications. However, the typical fabrication
process for PSC development to date is performed in an inert atmosphere
(nitrogen), usually in a glovebox, hampering the industrial scale-up.
In this work, we demonstrate, for the first time, the use of double-cation
perovskite (forsaking the unstable methylammonium (MA) cation) processed
in ambient air by employing potassium-doped graphene oxide (GO-K)
as an interlayer, between the mesoporous TiO2 and the perovskite
layer and using infrared annealing (IRA). We upscaled the device active
area from 0.09 to 16 cm2 by blade coating the perovskite
layer, exhibiting power conversion efficiencies (PCEs) of 18.3 and
16.10% for 0.1 and 16 cm2 active area devices, respectively.
We demonstrated how the efficiency and stability of MA-free-based
perovskite deposition in air have been improved by employing GO-K
and IRA.
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