Fused‐ring electron acceptors (FREAs), as a family of non‐fullerene (NF) acceptors, have achieved tremendous success in pushing the power conversion efficiency of organic solar cells. Here, the ...detailed molecular packing motifs of two extensively studied FREAs—ITIC and ITIC‐Th are reported. It is revealed for the first time the long‐range structure ordering along the backbone direction originated from favored end group π–π stacking. The backbone ordering could be significantly enhanced in the ternary film by the mutual mixing of ITIC and ITIC‐Th, which gives rise to an improved in‐plane electron mobility and better ternary device performance. The backbone ordering might be a common morphological feature of FREAs, providing explanations to previously observed small open circuit voltage loss and superior performance of FREA‐based devices and guiding the future molecular design of high‐performance NF acceptors.
The existence of the long‐range backbone ordering in films based on fused‐ring electron acceptors—ITIC and ITIC‐Th—is revealed. The backbone ordering, originated from the favored end group π–π stacking, could be significantly enhanced in the ternary PBDB‐T:ITIC:ITIC‐Th film and results in improved in‐plane electron mobility and device performance.
Naphtho1,2‐b:5,6‐b′dithiophene is extended to a fused octacyclic building block, which is end capped by strong electron‐withdrawing 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile ...to yield a fused‐ring electron acceptor (IOIC2) for organic solar cells (OSCs). Relative to naphthalene‐based IHIC2, naphthodithiophene‐based IOIC2 with a larger π‐conjugation and a stronger electron‐donating core shows a higher lowest unoccupied molecular orbital energy level (IOIC2: −3.78 eV vs IHIC2: −3.86 eV), broader absorption with a smaller optical bandgap (IOIC2: 1.55 eV vs IHIC2: 1.66 eV), and a higher electron mobility (IOIC2: 1.0 × 10−3 cm2 V−1 s−1 vs IHIC2: 5.0 × 10−4 cm2 V−1 s−1). Thus, IOIC2‐based OSCs show higher values in open‐circuit voltage, short‐circuit current density, fill factor, and thereby much higher power conversion efficiency (PCE) values than those of the IHIC2‐based counterpart. In particular, as‐cast OSCs based on FTAZ: IOIC2 yield PCEs of up to 11.2%, higher than that of the control devices based on FTAZ: IHIC2 (7.45%). Furthermore, by using 0.2% 1,8‐diiodooctane as the processing additive, a PCE of 12.3% is achieved from the FTAZ:IOIC2‐based devices, higher than that of the FTAZ:IHIC2‐based devices (7.31%). These results indicate that incorporating extended conjugation into the electron‐donating fused‐ring units in nonfullerene acceptors is a promising strategy for designing high‐performance electron acceptors.
A novel fused‐ring electron acceptor (IOIC2) based on naphthodithiophene is designed and synthesized, and compared with a naphthalene‐based counterpart (IHIC2). The IOIC2‐based single‐junction binary‐blend organic solar cells exhibit efficiencies up to 12.3%, much higher than that of IHIC2 (7.45%).
Modest exciton diffusion lengths dictate the need for nanostructured bulk heterojunctions in organic photovoltaic (OPV) cells; however, this morphology compromises charge collection. Here, we reveal ...rapid exciton diffusion in films of a fused-ring electron acceptor that, when blended with a donor, already outperforms fullerene-based OPV cells. Temperature-dependent ultrafast exciton annihilation measurements are used to resolve a quasi-activationless exciton diffusion coefficient of at least 2 × 10–2 cm2/s, substantially exceeding typical organic semiconductors and consistent with the 20–50 nm domain sizes in optimized blends. Enhanced three-dimensional diffusion is shown to arise from molecular and packing factors; the rigid planar molecular structure is associated with low reorganization energy, good transition dipole moment alignment, high chromophore density, and low disorder, all enhancing long-range resonant energy transfer. Relieving exciton diffusion constraints has important implications for OPVs; large, ordered, and pure domains enhance charge separation and transport, and suppress recombination, thereby boosting fill factors. Further enhancements to diffusion lengths may even obviate the need for the bulk heterojunction morphology.
A fused-ring electron acceptor based on indacenodithiophene (IDIC) was used to replace TiO
2
and work as an electron transport layer in planar n–i–p perovskite solar cells. IDIC improves perovskite ...crystallinity and film quality due to its hydrophobicity and incompatible wetting surface. IDIC facilitates electron extraction and transport due to its high mobility and suitable energy levels matched with the perovskite. IDIC reduces charge recombination in the devices due to trap passivation at the perovskite surface. The IDIC-based devices exhibit a champion power conversion efficiency of 19.1%, which is higher than that of TiO
2
-based devices (17.4%). Moreover, the device stability is significantly improved by IDIC.
Charge extraction in organic solar cells (OSCs) is commonly believed to be limited by bimolecular recombination of photogenerated charges. However, the fill factor of OSCs is usually almost entirely ...governed by recombination processes that scale with the first order of the light intensity. This linear loss was often interpreted to be a consequence of geminate or trap-assisted recombination. Numerical simulations show that this linear dependence is a direct consequence of the large amount of excess dark charge near the contact. The first-order losses increase with decreasing mobility of minority carriers, and we discuss the impact of several material and device parameters on this loss mechanism. This work highlights that OSCs are especially vulnerable to injected charges as a result of their poor charge transport properties. This implies that dark charges need to be better accounted for when interpreting electro-optical measurements and charge collection based on simple figures of merit.
Owing to the lightweight, flexibility, and molecular diversity, organic photothermal materials are considered promising solar absorbent materials for water‐evaporating purification. Herein, we ...utilize the blend of two organic conjugated photothermal materials, PM6 and Y6, with broadband solar absorption from 350 to 1000 nm and high‐efficiency photothermal properties to fabricate a Janus water evaporator on cellulose paper. Similar to the asymmetric wetting behavior on the lotus leaf, the evaporator shows efficient water adhesion on the bottom surface and water repellency on the top surface for a desirable self‐floating capability and salt resistance. With a mass of only 0.5 mg per 3.14 cm2, the PM6:Y6 blend‐based water evaporator achieves 88.9% of solar thermal conversion efficiency (η) and 1.52 kg m−2 h−1 of solar water evaporation rate (m) under 1.0 kW m−2 solar irradiation. These properties are almost the best performance among purely organic water evaporators especially with such a premise of material saving. The concentrations of primary ions are significantly decreased by 4–6 orders after desalination, accompanied by excellent performance for wastewater treatment. This evaporator realizes a m of 1.21 kg m−2 h−1, a η of 75.7%, and a voltage of 61 mV under one sun irradiation by assembling with a thermoelectric equipment. This study demonstrates that the blending of PM6 and Y6 achieves photothermal synergism, which improves the photothermal property and water evaporation rate, providing a valuable prospect for their application in water purification and thermoelectric power generation.
A Janus water evaporator with desirable self‐floating capability and salt resistance was fabricated by bandgap blending of two organic conjugated photothermal materials. The properties of this broadband evaporator are almost the best among purely organic water evaporators especially with such a premise of material saving. This photothermal evaporator also realizes the synergistic effect of photothermal evaporation and thermoelectric power generation.
We compared an indacenodithiophene(IDT)-based fused-ring electron acceptor IDIC1 with its counterpart IHIC1 in which the central benzene unit is replaced by a naphthalene unit, and investigated the ...effects of the benzene/naphthalene core on the optical and electronic properties as well as on the performance of organic solar cells (OSCs). Compared with benzene-cored IDIC1, naphthalene-cored IHIC1 shows a larger π-conjugation with stronger intermolecular π–π stacking. Relative to benzene-cored IDIC1, naphthalene-cored IHIC1 shows a higher lowest unoccupied molecular orbital energy level (IHIC1: −3.75 eV, IDIC1: −3.81 eV) and a higher electron mobility (IHIC1: 3.0 × 10
−4
cm
2
V
−1
s
−1
, IDIC1: 1.5 × 10
−4
cm
2
V
−1
s
−1
). When paired with the polymer donor FTAZ that has matched energy levels and a complementary absorption spectrum, IHIC1-based OSCs show higher values of open-circuit voltage, short-circuit current density, fill factor and power conversion efficiency relative to those of the IDIC1-based control devices. These results demonstrate that extending benzene in IDT to naphthalene is a promising approach to upshift energy levels, enhance electron mobility, and finally achieve higher efficiency in nonfullerene acceptor-based OSCs.
We extend thieno3,2-
b
thiophene and naphthalene cores in our previously reported fused-ring electron acceptors (FREAs) F6IC and IHIC2 to benzo
b
benzo4,5thieno2,3-
d
thiophene and naphtho1,2-
b
...:5,6-
b
′dithiophene, respectively, and synthesize two new isomeric FREAs BTIC and NTIC. Both BTIC and NTIC exhibit strong absorption from 500 to 800 nm with high extinction coefficients (2.4-2.6 × 10
5
M
−1
cm
−1
) and electron mobilities of 1.8-3.4 × 10
−4
cm
2
V
−1
s
−1
. Paired with the polymer donor PM6, the BTIC and NTIC-based organic solar cells (OSCs) show power conversion efficiencies (PCEs) of 11.5-12.2%, much higher than those of the control devices based on IHIC2 and F6IC (7.21-7.31%). The PM6/NTIC-based OSCs afford a higher PCE of 12.2% than PM6/BTIC-based OSCs (11.5%), due to the red-shifted absorption and up-shifted HOMO of NTIC.
We synthesize 2 new isomeric fused-ring electron acceptors BTIC and NTIC. BTIC and NTIC-based organic solar cells show power conversion efficiencies of 11.5-12.2%.
Efficient charge generation is a prerequisite to achieve high power conversion efficiency (PCE) in organic/polymer solar cells (OSCs/PSCs), which involves photoinduced electron transfer and/or hole ...transfer between the donor/acceptor interface upon photoexcitation. A high yield of charge from both processes usually requires sufficient energy offset between the donor and acceptor for charge separation, fast transport, and extraction for charge collection, as well as significant absorption complementation to maximize photon harvest. Here we demonstrate highly efficient PSCs with efficient dual photocurrent generation pathways from a blend of a polymer donor and two narrow-bandgap nonfullerene acceptors, with an outstanding certified PCE of 13.0% (verified as 12.5%) in PSCs with single-junction device architecture. The devices from these material systems show nonradiative recombination loss of ∼0.22–0.24 V, one of the smallest values for OSCs achieved so far and comparable to those of solar cells based on monocrystalline Si or metal-halide perovskites. This study highlights that dual charge generation pathways with high yield and strongly reduced voltage loss are indispensable for further increasing the PCE of OSCs.
Four fused-ring electron acceptors composed of the same naphtho1,2-
b
:5,6-
b
′dithiophene-based core and 3-(1,1-dicyanomethylene)-5,6-difluoro-1-indanone end groups without or with hexyloxyl groups ...on the core and/or phenyl side chains are compared to systematically study the effects of alkoxylation position on the molecular packing, optical, electronic, and photovoltaic properties of the nonfullerene acceptors. Alkoxylation on the core red-shifts absorption and reduces bandgap, while that on side chains has little effect on absorption and bandgap. Alkoxylation on the core up-shifts the HOMO and down-shifts the LUMO, while that on side chains shows very little effect on the energy levels. Alkoxylation on the core slightly improves electron mobility relative to that on the side chains. Both methods of alkoxylation decrease open-circuit voltage, but increase short-circuit current density and fill factor, leading to improved efficiencies of the organic solar cells. Finally, when blended with the polymer donor
PM6
,
IOIC3
/
IOIC4
with alkoxylation on the core or side chains yields efficiencies of 11.1-12.8%, which are higher than that of
IOIC2
without alkoxylation (10.5%).
IOIC5
with alkoxylation on both the core and side chains yields the highest efficiency of 13.8%.
Four fused-ring electron acceptors composed of the same core and end groups without or with hexyloxyl groups on the core and/or phenyl side chains are compared to systematically study the effects of alkoxylation position on the molecular packing, optical, electronic, and photovoltaic properties of the nonfullerene acceptors.
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