Balanced Charge Carrier Research Articles

End Group Tuning in Acceptor–Donor–Acceptor Nonfullerene Small Molecules for High Fill Factor Organic Solar Cells

AbstractHigh fill factors have only recently become commonplace in nonfullerene‐based organic solar cells, with the balance of charge carrier mobilities often cited as the contributing factor. Here an end‐group modification to a commonly used nonfullerene acceptor (O‐IDTBR) is reported, in which the rhodanine end groups are replaced with dicyano moieties, resulting in the acceptor O‐IDTBCN. This new acceptor affords significant improvement in the fill factor (73%) and photocurrent (19.8 mA cm−2) in organic solar cells with the low bandgap polymer PTB7‐Th. A narrowing of the bandgap, as a result of greater push–pull hybridization, allows complementary absorption to the donor and thus improved photon harvesting. Additionally, the measurement of charge carrier mobilities and lifetimes in both systems reveal that the PTB7‐Th:O‐IDTBCN blend possesses more balanced charge carrier mobilities, and longer lifetimes. Morphology studies reveal a slightly greater degree of molecular mixing of the O‐IDTBCN when blended with PTB7‐Th, despite the greater and more balanced charge carrier mobilities in this blend.

Solution Process Feasible Highly Efficient Organic Light Emitting Diode with Hybrid Metal Oxide Based Hole Injection/Transport Layer

Organic light emitting diodes (OLEDs) have drawn great attention owing to their potential applications in high-quality flat display panels and smart solid-state lighting. Over the last three decades, numerous approaches have been made on material design and device physics to achieve high-efficiency and long-lifespan. Herein, we report a novel tactic to employ solution-processed hybrid metal oxide, molybdenum trioxide-tungsten trioxide (MoO3:WO3), as an efficient and stable hole injection/transport (HIL/HTL) and electron blocking layer for efficient OLEDs. By using phosphorescent orange-red emitter tris(2-phenylquinoline)-iridium(III) Ir(2-phq)3, MoO3:WO3 HIL based OLED device exhibits a power efficiency of 27.7 lm W-1 and 22.9 lm W-1 at 100 and 1000 cd m-2, respectively, which are 89% and 157% higher than that of conventional OLED device consisting of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as an HIL. Moreover, the resulted device also displays 1.6 times lower turn-on voltage and 3.0 time higher brightness as compare to other counter part. The higher device performances of OLED device may be attributed to robust hole transporting ability, balanced charge carrier in the recombination zone and non-acidic nature of designed HIL. Our results demonstrate that a novel alternative approach based on transition metal oxide hybrid HIL/HTL as a substitute to PEDOT:PSS for high-efficiency solution process OLEDs.

Star-Shaped Magnesium Tetraethynylporphyrin Bearing Four Peripheral Electron-Accepting Functionalities for Organic Solar Cell

Magnesium tetraethynylporphyrins bearing four electron-deficient diketopyrrolopyrrole (DPP; Mg-TEP-DPP4) units were synthesized by Sonogashira coupling, andtheir optical and electrochemical properties were investigated. The energy levels were effectively tuned by DPP with or without electron-withdrawing end-caps. Importantly, all the Mg-TEP-DPP4moleculeshave broad absorption bands across the visible and near-infrared regions. The time-dependent excited state features of Mg-TEP-DPP4molecules and their kinetics wereinvestigatedby femtosecond transient absorption spectroscopy in combination with multiwavelength and global/target analyses of time-resolved spectra. Importantly, the charge-separated state was demonstrated to undergo recombination within 253 ps in benzonitrile. Bulk heterojunction organic solar cells fabricated with Mg-TEP-DPP4:PC61BM exhibited a power conversion efficiencyof 7.40% after solvent vapor annealing, which enabled balanced charge carrier transport, reduced charge recombination, and favorable charge separation and collection.

Efficient perovskite solar cells by hybrid perovskites incorporated with heterovalent neodymium cations

Recently, hybrid perovskite materials have emerged as attractive alternatives for realizing cost-effective efficient perovskite solar cells. To date, impressive efficiency has been realized from the state-of-the-art solar cells through generic interface engineering and film morphological manipulation of perovskite active-layer in macroscopic scale. To further boost the efficiency of perovskite solar cells, microscopically tuning optoelectronic properties of hybrid perovskite materials represents a promising direction. In this study, we report efficient perovskite solar cells by a novel hybrid perovskites material that is incorporated with heterovalent neodymium cations (Nd3+). As compared with pristine hybrid perovskite materials, Nd3+-doped hybrid perovskite materials possess superior film quality with highly reduced trap-states, significantly enlarged charge carrier lifetimes, dramatically enhanced and balanced charge carrier mobilities. As a result, planar heterojunction perovskite solar cells by Nd3+-doped hybrid perovskite materials exhibit highly reproducible power conversion efficiency of 21.15% and significantly suppressed photocurrent hysteresis. These findings open a new window of tuning the optoelectronic properties of hybrid perovskite materials and boosting the device performance of perovskite solar cells. 21.15% power conversion efficiency and significantly suppressed photocurrent hysteresis were demonstrated from planar heterojunction perovskite solar cell using heterovalent neodymium cation doped hybrid perovskite materials.

47-Fold EQE improvement in CsPbBr3 perovskite light-emitting diodes via double-additives assistance

All-inorganic cesium halide perovskite materials are intensively investigated due to their excellent photoelectric characteristics, but poor film coverage, unbalanced charge carrier transporting and insufficient exciton harvesting are remaining challenges to be overcome in order to achieve high electroluminescent (EL) performance in perovskite light-emitting diodes (PeLEDs). Here we show that these problems can be solved by introducing both a phosphorescent sensitizer (FIrpic) and an electron transporting material (TmPyPB) into all-inorganic cesium halide perovskite (CsPbBr 3 ). And highly efficient green PeLEDs with full coverage CsPbBr 3 :TmPyPB:FIrpic film as the emissive layer have been achieved, exhibiting the maximum luminance of 37784 cd/m 2 , the maximum current efficiency of 22.6 cd/A and the corresponding maximum external quantum efficiency (EQE) of 5.85%, where the EQE is 48-fold to that of bare CsPbBr 3 PeLEDs. The enhanced EL performance is attributed to less non-radiative current leakage, better film surface passivation effect, balanced charge carrier injection and transportation, as well as better exciton harvesting. It is believed that our work will provide an effective strategy to further improve EL performance of PeLEDs via better exciton harvesting. • Excellent enhanced electroluminescent performances were realized in CsPbBr 3 :TmPyPB:FIrpic based PeLEDs. • Pinhole-free and continuous CsPbBr 3 :TmPyPB:FIrpic perovskite films was achieved. • The current leakage was largely reduced. • More balanced charge carrier transporting behavior in perovskite emitting layer was reached. • Improved exciton harvesting was realized due to Förster and Dexter energy transfer processes.

Charge carrier transport and nanomorphology control for efficient non-fullerene organic solar cells

Single junction organic photovoltaic devices (OPVs) have exceeded 15% power conversion efficiency (PCE) with the help of fused ring based low-bandgap non-fullerene acceptors (NFAs). As a major type of NFA, the indacenodithiophene derivative NFA (IDTBR) has been shown to have superior OPV stability with outstanding VOC, but the efficiency is relatively lower compared to the reported OPV champion devices. Further improvements towards high efficiencies in this OPV system remains challenging due to the relatively poor charge carrier transport properties in the bulk heterojunction film, particularly the electron transport in small molecule non-fullerene acceptor network. Here we conducted detailed study on the dependence of carrier transport on BHJ donor–acceptor (D–A) composition. Our results show that the nano-morphology or phase aggregation of non-fullerene acceptor (NFA) molecules can be tuned via D–A composition in bulk heterojunction layer, and the improvement of electron mobility was shown to be enhanced by almost one order – from 1.23 × 10−6 cm2/V (D:A = 1:1 by weight) to 1.02 × 10−5 cm2/V (D:A = 1:2) – due to the improved connectivity of electron transport pathways. Further increase of NFA component content, however, has led to over-sized phase segregation, deteriorating the photovoltaic performance of organic soar cells. The optimized BHJ cell shows more balanced charge carrier transport and phase segregation, which yields a PCE of 10.79%. Furthermore, it shows a VOC as high as 1.03 V, which is ascribed to the significantly suppressed radiative and non-radiative recombination losses with bandgap-VOC offset Eg/q-VOC of only 0.55 V.

Highly efficient phosphorescent organic light-emitting diodes based on single-layer structure.

We demonstrated highly efficient single-layer organic light-emitting diodes (OLEDs) based on graded-composition architecture. The single-layer OLEDs comprise graded-composition from a mostly hole-transport material at anode to a mostly electron-transport material at cathode. The resulting device with low turn-on voltage of 2.85V shows maximum power efficiency and current efficiency of 44.8lm/W and 42.7cd/A, respectively. It is found that the emission dopant plays an important role to obtain more balanced charge carriers, causing the recombination zone slightly shift to the center of the device. The results of our work suggest that the graded-composition structure represents a path to achieving highly efficient single-layer OLEDs.

Inkjet-Printed High-Efficiency Multilayer QLEDs Based on a Novel Crosslinkable Small-Molecule Hole Transport Material.

Quantum dots light-emitting diodes (QLEDs) have attracted much interest owing to their compatibility with low-cost inkjet printing technology and potential for use in large-area full-color pixelated display. However, it is challenging to fabricate high efficiency inkjet-printed QLEDs because of the coffee ring effects and inferior resistance to solvents from the underlying polymer film during the inkjet printing process. In this study, a novel crosslinkable hole transport material, 4,4'-bis(3-vinyl-9H-carbazol-9-yl)-1,1'-biphenyl (CBP-V) which is small-molecule based, is synthesized and investigated for inkjet printing of QLEDs. The resulting CBP-V film after thermal curing exhibits excellent solvent resistance properties without any initiators. An added advantage is that the crosslinked CBP-V film has a sufficiently low highest occupied molecular orbital energy level (≈-6.2 eV), high film compactness, and high hole mobility, which can thus promote the hole injection into quantum dots (QDs) and improve the charge carrier balance within the QD emitting layers. A red QLED is successfully fabricated by inkjet printing a CBP-V and QDs bilayer. Maximum external quantum efficiency of 11.6% is achieved, which is 92% of a reference spin-coated QLED (12.6%). This is the first report of such high-efficiency inkjet-printed multilayer QLEDs and demonstrates a unique and effective approach to inkjet printing fabrication of high-performance QLEDs.

Charge-carrier behavior in Ba-, Sr- and Yb-filled CoSb3 : NMR and transport studies

We report $^{59}$Co NMR and transport measurements on $n$-type filled skutterudites Ba$_x$Yb$_y$Co$_4$Sb$_{12}$ and $A$$_x$Co$_4$Sb$_{12}$ ($A$= Ba, Sr), promising thermoelectric materials. The results demonstrate consistently that a shallow defect level near the conduction band minimum dominates the electronic behavior, in contrast to the behavior of unfilled CoSb$_3$. To analyze the results, we modeled the defect as having a single peak in the density of states, occupied at low temperatures due to donated charges from filler atoms. We fitted the NMR shifts and spin-lattice relaxation rates allowing for arbitrary carrier densities and degeneracies. The results provide a consistent picture for the Hall data, explaining the temperature dependence of the carrier concentration. Furthermore, without adjusting model parameters, we calculated Seebeck coefficient curves, which also provide good consistency. In agreement with recently reported computational results, it appears that composite native defects induced by the presence of filler atoms can explain this behavior. These results provide a better understanding of the balance of charge carriers, of crucial importance for designing improved thermoelectric materials.

Surface Ligand Engineering for Efficient Perovskite Nanocrystal-Based Light-Emitting Diodes.

Lead halide perovskites (LHPs) are emerging as promising materials for light-emitting device applications because of the tunability of the band gap, narrow emission, solution processability, and flexibility. Typically, LHP nanocrystals (NCs) with surface ligands show high photoluminescence quantum yields because of charge-carrier confinement with higher exciton binding energy ( Eb). However, the conventionally used oleylamine (OAm) ligands result in the low electrical conductivity and stability of perovskite NCs (PNCs) because of a long carbon chain without conjugation bonds and weak interaction with the surface of NCs. Here, we report the effect of bulkiness and chain length of ligand materials on the properties and stability of CsPbBr3 PNCs by replacing OAm with other suitable ligands. The effect of the bulkiness of quaternary ammonium bromide (QAB) ligands was systemically studied. The less bulky QAB ligands surrounded the surface of NCs effectively, and brought better surface passivation and less aggregation compared to bulky QAB ligands, and finally the optical property and stability of CsPbBr3 PNCs were enhanced. Furthermore, the electrical property of CsPbBr3 PNCs was optimized by tuning the long-chain length of QAB ligands for balanced charge-carrier transport. Finally, we achieved highly efficient green emissive CsPbBr3 PNC light-emitting diodes (LEDs) by using PNCs with optimized didecyldimethyl ammonium bromide ligands with a current efficiency of 31.7 cd A-1 and external quantum efficiency of 9.7%, which were enhanced 16-fold compared to those of CsPbBr3 LEDs using PNCs with conventional OAm ligands.

Cation influence on carrier dynamics in perovskite solar cells

Rubidium and Cesium cations (Rb+ and Cs+) incorporation recently emerged as a viable strategy to enhance perovskite solar cells (PSCs) efficiency. However, a clear understanding of the impact of these cations on the structure-function relationship in relation to the device performance is severely lacking. Here, we systematically investigate the influence of Rb+ and Cs+ on the carrier dynamics using transient optical spectroscopy and correlate with solar cell performance. Unlike Rb+, Cs+ integrates well with methylammonium (MA+) and formamidinium (FA+) yielding increased perovskite grain size, longer charge carrier lifetimes and improved power conversion efficiency (PCE). Concomitant incorporation of Cs+/Rb+ cooperatively retards radiative recombination by ~60% in the quaternary-cation based perovskite system (RbCsMAFA) compared to the dual-cation MAFA samples. By suppressing the defect density, PCEs around 20% are obtained along with more balanced charge carrier diffusion length and comparable photoluminescence quantum yield in quaternary-cation perovskites. While the synergistic addition of Rb+ and Cs+ is attractive for controlling defects and recombination losses in efficient solar cells development, sole incorporation of Rb+ is still an engineering challenge. Importantly, our study explicates the underlying mechanisms behind the synergistic combination of cations to minimize the charge carrier losses and achieve high efficiency perovskite solar cells.

Realizing efficient bipolar deep-blue light-emitting poly(2,7-carbazole) derivatives by suppressing intramolecular charge transfer

Two series of twisted bipolar poly(2,7-carbazole) derivatives, namely PCz-37RSOs and PCz-28SOs, were synthesized by introducing electron-deficient 2,8-dioctyl- dibenzothiophene-S,S-dioxide-3,7-diyl (37RSO) and dibenzothiophene- S,S –dioxide −2,8-diyl (28SO) unit into poly(9-heptadecanyl-2,7-carbazole) (PCz) backbone, respectively. The incorporation of electron-withdrawing 37RSO and 28SO into PCz backbone decreased effective conjugation length, and further restrained charge transfer effect existed in dipolar system, simultaneously, the balanced charge carrier injection/transportation were realized due to the eletrophilicity of SO unit. Consequently, the resulting polymers showed hypsochromic shift and narrowed emission spectra regarding to PCz-37SOs that contains linear SO unit in main chain, and exhibited balanced hole/electron fluxes with respect to PCz in the range of 0–10 V. The single-layer devices based on resulting bipolar polymers exhibited excellent electroluminescent spectra stability in the current densities from 100 to 400 mA cm−2, and displayed deep blue electroluminescence spectra with the Commission Internationale de L’ Eclairage (CIE) of (0.16, 0.07) for PCz-37RSO5 and (0.16, 0.09) for PCz-28SO5. The superior device performance was achieved with the maximum luminous efficiency (LEmax) of 2.69 cd A−1 for PCz-28SO20, which obviously outperformed that of 0.24 cd A−1 for PCz. These results indicated that twisted molecular structure design is a promising strategy for efficient deep blue light-emitting polymers.

Reduced Efficiency Roll-Off in White Phosphorescent Organic Light-Emitting Diodes Based on Double Emission Layers.

We demonstrate high-efficiency white phosphorescent organic light-emitting diodes with low efficiency roll-off. The feature of the device concept is employing two phosphorescent emission layers (EMLs) separated by a mixed interlayer. Both the EMLs are doped by two phosphorescent dyes. The resulting white device with the optimized doping concentration shows a maximum efficiency of 31.0 cd/A with extremely low efficiency roll-off of 30.7 cd/A at 1000 cd/m2, 27.2 cd/A at 5000 cd/m2, and 25.5 cd/A at 10,000 cd/m2, respectively, without any outcoupling structures. This is enabled by the balanced charge carrier transport in EMLs, leading to broader exciton recombination zone.

Critical roles of potassium in charge-carrier balance and diffusion induced defect passivation for efficient inverted perovskite solar cells

Critical roles of potassium in charge-carrier balance and diffusion induced defect passivation for highly efficient inverted PSCs are revealed.

Wide bandgap donor-acceptor conjugated polymers with alkylthiophene as side chains for high-performance non-fullerene polymer solar cells

Abstract Four wide bandgap donor-acceptor (D-A) conjugated polymers, i.e. P-diF2T, P-TT, P-BDT and P-NDT, with bis(5-(2-decyltetradecyl)-[2,3′-bithiophen]-2′-yl)arylenes as D-units and 2-propyl-5,6-difluorobenzo[d][1,2,3]triazole (ffTAZ) as A unit were synthesized for photovoltaic applications. In P-diF2T, P-TT, P-BDT and P-NDT, 3,3′-difluoro-2,2′-bithiophene (diF2T), thieno[3,2-b]thiophene (TT), benzo[1,2-b:4,5-b']dithiophene (BDT) and naphtho[1,2-b:5,6-b']dithiophene (NDT) were used as aryl central units, respectively, to adjust the properties of the polymers. The optical bandgap is 1.83 eV for P-diF2T, 1.85 eV for P-TT, 1.90 eV for P-BDT and 2.04 eV for P-NDT. All four polymers show temperature-dependent aggregation behavior in solution, and their absorption spectra are complementary with that of non-fullerene acceptor (NFA) 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(5-hexylthiophen-2-yl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC-Th). Polymer solar cells (PSCs) based on these polymers and ITIC-Th were fabricated and characterized. Power conversion efficiencies (PCEs) higher than 7% were demonstrated for all polymers. The devices based on P-diF2T exhibited the highest PCE up to 10.08% with a high fill factor (FF) of 0.741. The good photovoltaic performance of P-diF2T is attributed to the synergies of the low-lying highest occupied molecular orbital (HOMO) energy level of the polymer and the favorable microstructures and morphology and thereby high and balanced charge carrier mobilities of the blend films. This study suggested that adjusting aromatic D units together with using alkylthiophene as side chains is an effective approach to design donor polymers for high performance PSCs based on NFA.

Control of Interface Defects for Efficient and Stable Quasi-2D Perovskite Light-Emitting Diodes Using Nickel Oxide Hole Injection Layer.

Metal halide perovskites (MHPs) have emerged as promising materials for light‐emitting diodes owing to their narrow emission spectrum and wide range of color tunability. However, the low exciton binding energy in MHPs leads to a competition between the trap‐mediated nonradiative recombination and the bimolecular radiative recombination. Here, efficient and stable green emissive perovskite light‐emitting diodes (PeLEDs) with an external quantum efficiency of 14.6% are demonstrated through compositional, dimensional, and interfacial modulations of MHPs. The interfacial energetics and optoelectronic properties of the perovskite layer grown on a nickel oxide (NiOx) and poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate hole injection interfaces are investigated. The better interface formed between the NiOx/perovskite layers in terms of lower density of traps/defects, as well as more balanced charge carriers in the perovskite layer leading to high recombination yield of carriers are the main reasons for significantly improved device efficiency, photostability of perovskite, and operational stability of PeLEDs.

Benzodithiophene-Dithienylbenzothiadiazole Copolymers for Efficient Polymer Solar Cells: Side-Chain Effect on Photovoltaic Performance.

A new series of low band gap D-A alternating polymers based on 4,5-bis((2-ethylhexyl)oxy)benzo[2,1- b:3,4- b']dithiophene (BDT) and 5-fluoro-4,7-bis(4-alkylthien-2-yl)benzo[ c][1,2,5]thiadiazole bearing different size of lateral alkyl substituents, namely, PfBB- n, n = 8, 10, 12, 14, and 16, was designed and synthesized for high-performance bulk heterojunction (BHJ) polymer solar cells (PSCs). PfBB- n-bearing linear alkyl side chains exhibited strong and controllable aggregation in both solution and solid states, which gives rise to a significant bathochromic shift of the absorption cut-off down to ∼780 nm in thin film. In addition, the strong and wide absorption (350-800 nm) of PfBB- n polymers can compensate for the relatively weak absorption of PC71BM, particularly in the 300-400 range nm to enhance light harvesting of such an active blend. BHJ solar cells based on PfBB- n:PC71BM blends as an active layer showed power conversion efficiency (PCE) in the range 7.8-9.7%. Because of the strong stacking interchain interactions, PfBB-12-based PSC exhibited aggregation-induced spectral broadening, superior structural order, higher exciton dissociation, higher and more balanced charge carrier mobilities, as well as reduced recombination losses. As a result, PfBB-12-based device afforded the best PCE of 9.7%, with the highest short-circuit current density ( Jsc) of 16.6 mA cm-2 and open-circuit voltage ( Voc) of 0.92 V among devices fabricated. These results demonstrate that the alkyl side chain of the polymer significantly affects the absorption, morphology, and electronic properties of the active blend of PfBB- n/PC71BM, which would provide an alternative useful tool to fine-tune the device performance. Our results also highlight that the electron-rich benzo[2,1- b:3,4- b']dithiophene building block, BDT, is highly useful for the construction of low band gap D-A polymer for highly efficient PSCs.

Preferential Orientation of Tetrahedral Silicon-Based Hosts in Phosphorescent Organic Light-Emitting Diodes.

Vacuum-processed diphenylbis(3-(pyridine-2-yl)phenyl)silane (2PTPS), diphenylbis(3-(pyridine-3-yl)phenyl)silane (3PTPS), and diphenylbis(3-(pyridine-4-yl)phenyl)silane (4PTPS) have been used as electron-transporting host materials combined with tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as the hole-transporting host, which induce balanced charge carrier transport for high-efficiency phosphorescent organic light-emitting diodes. The 4PTPS-based organic light-emitting diodes with tris[2-phenylpyridinato-C2,N]iridium(III) [Ir(ppy)3] dopant showed highest current efficiency and external quantum efficiency of 53.54 cd/A and 15.61%, compared to 2PTPS (40.75 cd/A, 11.84%) and 3PTPS (29.35 cd/A, 8.54%). These results were attributed to the well-aligned structure with preferential horizontal orientation of the emitting material layer by the diffraction intensity distribution as a function of azimuthal angle in two-dimensional grazing incidence X-ray diffraction analysis. The molecular orientation of TCTA:4PTPS material with a narrow azimuthal intensity distribution had better priority to the horizontal direction than the other TCTA:2PTPS and TCTA:3PTPS materials, which is related to the charge transport as well as the device efficiency. We found that the preferential horizontal orientation of the co-host material with a balanced charge carrier was not affected by Ir(ppy)3 dopant with a homoleptic structure and bis-[2-(4,6-difluorophenyl)pyridinato-N,C2](picolinato)iridium [Firpic] dopant with a heteroleptic structure in the co-host/dopant system.

All‐Solution‐Processed Pure Formamidinium‐Based Perovskite Light‐Emitting Diodes

All-solution-processed pure formamidinium-based perovskite light-emitting diodes (PeLEDs) with record performance are successfully realized. It is found that the FAPbBr3 device is hole dominant. To achieve charge carrier balance, on the anode side, PEDOT:PSS 8000 is employed as the hole injection layer, replacing PEDOT:PSS 4083 to suppress the hole current. On the cathode side, the solution-processed ZnO nanoparticle (NP) is used as the electron injection layer in regular PeLEDs to improve the electron current. With the smallest ZnO NPs (2.9 nm) as electron injection layer (EIL), the solution-processed PeLED exhibits a highest forward viewing power efficiency of 22.3 lm W-1 , a peak current efficiency of 21.3 cd A-1 , and an external quantum efficiency of 4.66%. The maximum brightness reaches a record 1.09 × 105 cd m-2 . A record lifetime T50 of 436 s is achieved at the initial brightness of 10 000 cd m-2 . Not only do PEDOT:PSS 8000 HIL and ZnO NPs EIL modulate the injected charge carriers to reach charge balance, but also they prevent the exciton quenching at the interface between the charge injection layer and the light emission layer. The subbandgap turn-on voltage is attributed to Auger-assisted energy up-conversion process.

Morphology Control Enables Efficient Ternary Organic Solar Cells.

Ternary organic solar cells are promising alternatives to the binary counterpart due to their potential in achieving high performance. Although a growing number of ternary organic solar cells are recently reported, less effort is devoted to morphology control. Here, ternary organic solar cells are fabricated using a wide-bandgap polymer PBT1-C as the donor, a crystalline fused-ring electron acceptor ITIC-2Cl, and an amorphous fullerene derivative indene-C60 bisadduct (ICBA) as the acceptor. It is found that ICBA can disturb π-π interactions of the crystalline ITIC-2Cl molecules in ternary blends and then help to form more uniform morphology. As a result, incorporation of 20% ICBA in the PBT1-C:ITIC-2Cl blend enables efficient charge dissociation, negligible bimolecular recombination, and balanced charge carrier mobilities. An impressive power conversion efficiency (PCE) of 13.4%, with a high fill factor (FF) of 76.8%, is eventually achieved, which represents one of the highest PCEs reported so far for organic solar cells. The results manifest that the adoption of amorphous fullerene acceptor is an effective approach to optimizing the ternary blend morphology and thereby increases the solar cell performance.