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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. Graphical abstract Image 1 Highlights • Alkylthiophene was used as side chains to construct wide bandgap D-A conjugated polymers with ffTAZ as A unit. • With four different D units, the physicochemical and photovotaic properties and mophologies of the polymers were studied. • A high PCE up to 10.08% was achieved for PSC devices based on P-diF2T and ITIC-Th, with a high FF of 0.741. [ABSTRACT FROM AUTHOR]

Abstract The solid solutions comprising amorphous conjugated polymer PCDTBT and different fullerene derivatives, i.e. crystalline PC 71 BM and amorphous NC 60 BA, have been investigated. It is found that the solid solution based on NC 60 BA could produce more hole carriers at the room temperature due to a smaller activation energy from trap state to free carriers compared to that based on PC 71 BM. A higher hole carrier density could effectively fill traps and reduce the recombination loss during charge transport process. The solid solution based on PC 71 BM shows enhanced exciton dissociation probability at the solid solution/C 60 heterojunction interfaces. With combining the advantages of both the solid solutions, a small amount of amorphous NC 60 BA was introduced into the PCDTBT:PC 71 BM bulk heterojunction structure and the ternary BHJ PSCs composed of PCDTBT, PC 71 BM and NC 60 BA were fabricated. The ternary PSCs display outstanding photovoltaic performance compared to the binary PCDTBT:PC 71 BM bulk heterojunction PSCs. Graphical abstract With the same device structure, the ternary polymer solar cells based on the PCDTBT:NC 60 BA:PC 71 BM blend demonstrate much better photovoltaic performance than the binary PCDTBT:PC 71 BM blend solar cells. Image Highlights • The electrical and photovoltaic characteristic between the PCDTBT:NC 60 BA and PCDTBT:PC 71 BM solid solution are different. • The carrier density in PCDTBT:NC 60 BA solid solution is higher than that in PCDTBT:PC 71 BM solid solution. • The measured activation energy in PCDTBT:NC 60 BA solid solution is smaller than that in PCDTBT:PC 71 BM solid solution. • The ternary PSCs based on PCDTBT:NC 60 BA:PC 71 BM blend show superior photovoltaic performance to the binary PCDTBT:PC 71 BM PSCs. [ABSTRACT FROM AUTHOR]

Abstract The solid solution phenomenon in the amorphous PCDTBT:PC 71 BM blend was investigated. It has been disclosed that the PCDTBT:PC 71 BM blend with less than 20% PC 71 BM may form a kind of solid solution structure, which demonstrates a deeper HOMO level, a higher hole mobility, more free charges and less trap density than those of the pure PCDTBT film. It may well explain why the typical PCDTBT:PC 71 BM bulk heterojunction solar cells require higher PC 71 BM ratio to achieve a high power conversion efficiency. In that case, a portion of PC 71 BM is well intermixed with PCDTBT to form a solid solution phase and others form a pure PC 71 BM phase. It is the PCDTBT:PC 71 BM solid solution but not the pure PCDTBT to serve as the donor phases and to form interpenetrating networks with PC 71 BM phases. The PCDTBT:PC 71 BM solid solution phases favor to increase the V OC and enhance the charge collection leading to a high photovoltaic performance for the PCDTBT:PC 71 BM bulk heterojunction solar cells. Graphical abstract The PCDTBT:PC 71 BM blend with less than 20% PC 71 BM may form a kind of solid solution structure, which demonstrates a deeper HOMO level, a higher hole mobility, more free charges and less trap density than those of the pure PCDTBT film. A graphical schematic illustrates the interpenetrating networks composed of the solid solution and PC 71 BM in a practical PCDTBT:PC 71 BM BHJ solar cells. Image Highlights • The existence of the solid solution comprising of PCDTBT and PC 71 BM was confirmed by UPS and CV measurement. • Electric characteristics of the solid solution was studied by the FET and the varied temperature conductivity measurement. • The difference of photovoltaic characteristics between pure PCDTBT and the solid solution were compared. [ABSTRACT FROM AUTHOR]

Four fluorene-alt-di-2-thienyl-benzothiadiazole (FTBT) based oligomers with different number of repeated units are selected as electron acceptors in P3HT:oligomer solar cells. The effect of oligomer length on the phase separation behavior has been studied in detail. It is disclosed that the oligomer length strongly affects the film morphology and hence the exciton dissociation probability, charge transport as well as recombination characteristics. The short oligomer F1TBT1 is prone to aggregate and form large-scale phase separation which impedes exciton dissociation in the blend films. With increasing the acceptor length, large-scale aggregations are gradually suppressed due to the weakened migration ability of long FTBT oligomers in polymer matrix. Meanwhile, electron mobilities are enhanced with extending the oligomer length, which is favorable to suppress charge recombination in the blends. Finally, optimal photovoltaic performances with a PCE of 4.19% are achieved in P3HT:F3TBT3 based solar cell that compromises well between efficient exciton dissociation and balanced charge transport, which is almost three times higher than the F1TBT1 based device. This work highlights that tailoring the oligomer length can be used as an effective strategy to control phase separation and to enhance the photovoltaic performance in non-fullerene based polymer solar cells. [ABSTRACT FROM AUTHOR]

Formamidinium lead halide CH(NH 3 ) 2 PbX 3 (FAPbX 3 ) perovskite materials have achieved significant progress in efficient and stable single-junction/tandem perovskite solar cells, which is due to the promising thermal and air stability features. However, successful application of these materials in perovskite light-emitting diodes (PeLEDs) is scarce. Herein, regulating the FABr:PbBr 2 precursor concentration procedure is utilized to prepare very efficient PeLEDs based on CH(NH 3 ) 2 PbBr 3 (FAPbBr 3 ). The resultant FAPbBr 3 film prepared at optimized 10 wt% condition shows the satisfied exciton radiative rate and low nonradiative rate, and a high photoluminescent quantum yield. In combination with novel ethyl acetate (EA) anti-solvent spin-washing method, the resultant FAPbBr 3 film shows compact, uniform and high coverage morphology characteristics. The PeLEDs show a maximum current efficiency of 13.4 cd A −1 , an external quantum efficiency of 3.5%, a maximum luminance close to 10000 cd m −2 , and an extremely high power efficiency of 19.1 lm W −1 , respectively. This performance is the best among all reported on FAPbBr 3 type PeLEDs. [ABSTRACT FROM AUTHOR]

Efficient solution-processible yellow/orange emissive phosphors are highly required in solution-processed phosphorescent organic light-emitting diodes ( s -PhOLEDs). With respect to phenyl pyridine (ppy)-type Ir(III) complexes, 2-(9,9-diethylfluoren-2-yl)pyridine (Flpy)-type Ir(III) complexes have huge potential in yellow/orange s -PhOLEDs due to their extended conjugation and excellent solubility in common organic solvents. Herein, a new series of phosphorescent Ir(III) complexes, i.e. Ir(Flpy) 2 pic-N O, Ir(Flpy-CF 3 ) 2 pic-N O, Ir(Flpy-CF 3 ) 2 dbm and Ir(Flpy-CF 3 ) 2 acac, based on Flpy main ligand and picolinic N-oxide (pic-N O), acetylacetone (acac), and dibenzoyl methane (dbm) ancillary ligands are synthesized. The photophysical, electrochemical, and electroluminescent (EL) properties of these phosphorescent Ir(III) complexes are investigated in details. By introducing the CF 3 group in Flpy ligand and varying the ancillary ligands, the emission spectra of these phosphorescent complexes are tuned in a large range with EL emission peaks from 544 nm to 588 nm. The s -PhOLEDs employing these phosphors show promising EL performance with maximum external quantum efficiency (EQE) from 15.4% to 23.7% and high power efficiency from 61.9 l m W −1 to 80.4 l m W −1 . These highly efficient phosphorescent Ir(III) complexes may serve as ideal chromaticity components in solution-processed full-color displays and lighting devices. [ABSTRACT FROM AUTHOR]

The photovoltaic performance and stability of perovskite solar cells (PVSCs) is deeply dependent on the morphology of the perovskite film and the amount of lead iodide (PbI 2 ) residue. However, the morphology of perovskite film fabricated through two-step sequential deposition method usually suffers from poor film coverage and low crystallinity due to the ungovernable crystallization kinetics. Moreover, owing to the compact stacking of PbI 2 crystals, the conversion of PbI 2 is incomplete as well. In this work, we propose for the first time to control the nanostructure of PbI 2 to get high crystallinity, identical (100) crystal orientation and PbI 2 residue-free film. Porous PbI 2 with plate structure was obtained by selected solvent annealing (SSA). The reaction rate between PbI 2 and methylammonium iodide (MAI) was accelerated because the contact area between PbI 2 and MAI was enlarged due to the porous nanostructure of PbI 2 . Thus, uniform, high crystalline perovskite film without PbI 2 residue was obtained. Furthermore, (100) crystal orientation of perovskite was obtained due to the PbI 2 shape changing from grain to plate, which originated from the changing growth frontier of PbI 2 crystals. As a result, a promising power conversion efficiency of 16.61% is achieved in planar-heterojunction PVSCs due to improved photoabsorption and carrier extraction efficiency. This work for the first time establishes the relationship between PbI 2 structure and the corresponding structure of perovskite in detail, and shows a reasonable design of PbI 2 nanostructure is important to improve the perovskite morphology. [ABSTRACT FROM AUTHOR]

It is reported a kind of solution-processible transparent conductive film consisting of reduced graphene oxide (rGO) nanosheets and silver nanowires (AgNWs). The sandwiched structure of rGO/AgNWs/rGO is readily deposited via layer-by-layer blade-coating on the rigid glass or flexible PET substrate at mild annealing temperature. The rGO nanosheets sandwiching the AgNWs networks not only induce close contact of the AgNWs networks as a clipper to improve the conductivity, but also link the discrete AgNWs as a connector to improve the uniformity of the film conductivity. The transparent rGO/AgNWs/rGO film exhibits sheet resistance as low as 14.29 Ω/□ with transmittance over 90% at 550 nm. Moreover, the rGO/AgNWs/rGO composite film shows good ambient stability due to the rGO coverage and the existing charge interaction between AgNWs and rGO. Polymer solar cells are fabricated on the transparent rGO/AgNWs/rGO-coated glass or flexible PET substrates and they exhibit comparable photovoltaic perfromance to the control devices fabricated on the commercial ITO substrate. More importantly, the PSCs based on the rGO/AgNWs/rGO/PET substrate show more excellent flexibility than that of the device based on the ITO/PET substrate. [ABSTRACT FROM AUTHOR]

The proper crystallinity and a balance between H-aggregation and J-aggregation are both necessary for the best performance of small molecule organic solar cells. It is well known that J-aggregation is favorable to form more excitons due to its narrower bad-gap, leading to a high photocurrent. While H-aggregation has a higher lowest excited level which could provide stronger driving force for exciton dissociation. However, for 7,7′-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2- b :4,5- b ′]dithiophene-2,6-diyl)bis(6-fluoro-4(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[ c ][1,2,5]thiadiazole) ( p -DTS(FBTTh 2 ) 2 )/[6,6]-phenyl-C 71 -butyric acid methyl ester (PC 70 BM) blend system, the crystallinity is very low and p -DTS(FBTTh 2 ) 2 is mainly in J-aggregation. Thus, increasing H-aggregation of p -DTS(FBTTh 2 ) 2 is an effective way to improve photovoltaic efficiency of p -DTS(FBTTh 2 ) 2 /PC 70 BM system. In this paper, it was found that solvent vapor annealing (SVA) was an effective method to improve the crystallinity and the H-aggregation of p -DTS(FBTTh 2 ) 2 in blend film. Due to the prolonged time for self-organization, the crystallinity of p -DTS(FBTTh 2 ) 2 was enhanced. In addition, molecular motion ability of p -DTS(FBTTh 2 ) 2 was controlled and p -DTS(FBTTh 2 ) 2 could adjust its structure to form H-aggregation. As a result, the ratio of H/J could be tuned from 0.71 to 1.47 and the power conversion efficiencies (PCE) was improved from 2.64% to 6.63%. [ABSTRACT FROM AUTHOR]

Polymer solar cells (PSCs) based on the PBDTTT-EFT (polymer donor):N2200 (polymer acceptor) blend have been fabricated with the active layer processed with various solvents including o -dichlorobenzene ( o -DCB), chlorobenzene (CB), chloroform (CF), and CF: p -xylene (PX) mixed solvent. A highest power conversion efficiency (PCE) of 5.37% is achieved with the active layer processed with CF:PX mixed solvent. The dependence of short-circuit current density ( J SC ) on incident light intensity indicates that the charge recombination is to some extent suppressed in the device with the active layer processed with the CF:PX mixed solvent and results in an enhanced J SC . Morphology studies disclosed that the domains are preferential face-on orientation in the active layers processed with o -DCB, CB and CF, while it shows a combined face-on and edge-on orientation in CF:PX-processed film. The long-lived trap-assisted charge recombination originated from the active layer morphological variance has been focused on and investigated. And the nanosecond transient absorption experiment further demonstrated that the PBDTTT-EFT:N2200 film processed with o -DCB shows obvious long-lived trap-assisted charge recombination, while the trap-assisted charge recombination is effectively suppressed in the PBDTTT-EFT:N2200 film processed with CF:PX mixed solvent. This implies that deep localized traps correlated with the PBDTTT-EFT:N2200 morphology are reduced by using the CF:PX mixed solvent to process the active layer. In addition, the domains with a mixed orientation in the active layer may also enhance the three-dimensional charge transport and hence improve the charge-collection efficiency. [ABSTRACT FROM AUTHOR]

Abstract: The mechanisms for introduction of the additive to improve the poly(3-hexylthiophene) (P3HT):methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) organic solar cells performance are investigated. We add n-dodecylthiol to P3HT/PCBM solution and find that it both improves P3HT crystallinity and enhances P3HT/PCBM phase separation extent. UV–vis absorption spectroscopy (UV–vis) and dynamic light scattering (DLS) results reveal that n-dodecylthiol reduces the P3HT chains entanglement in the solution, which facilitates coil-to-rod transformation, a premise condition for P3HT crystallization. Also, it discloses that the influence of PCBM on the P3HT molecular interaction is diminished by adding n-dodecylthiol, this consequently benefits the P3HT crystallization during the film-forming process. Furthermore, the enhanced P3HT crystallinity reduces the PCBM amount which dissolved in the amorphous regions of P3HT, then promotes the aggregation of PCBM, which contributes to the controlled scale of phase segregation. Thus an increased P3HT crystallinity and a commensurate scale of phase separation balancing for exciton dissociation and charge transport and/or collection are finally obtained. This results in an almost threefold increase in device efficiencies when the volume fraction of additive is 2.0%, compared with reference devices without any additive in the photoactive layer as a consequence. [Copyright &y& Elsevier]

The optical waveguide effect limits strongly the light out-coupling efficiency in organic light-emitting diodes (OLEDs). Patterning the transparent ITO anode on the substrate is a potential way to weaken the optical waveguide effect and enhance the light-emitting efficiency of OLEDs. Herein, the one-dimensional (1D) and two-dimensional (2D) periodic patterned ITO/glass substrates have been successfully fabricated by using the holographic lithography technology and used to fabricate highly efficient OLEDs. The periodic micro-structured ITO layer could manipulate the total internal reflection at the organic/ITO interfaces and enhance the scattering effect so as to improve the light out-coupling efficiency. The effect of different micro-structured ITO layers on the light-emitting efficiency was investigated in a kind of orange phosphorescent OLEDs based on the m-MTDATA:Ir(Flpy-CF 3) 3 /TmPyPB emissive layer. The orange OLEDs employing the 1D grating and 2D lattice patterned ITO/glass substrates show the external quantum efficiencies (EQEs) of 25.12% and 29.61%, respectively. The orange OLEDs fabricated with the 2D hole patterned ITO glass substrate demonstrate the best light-emitting performance with a current efficiency of 100.55 cd A−1, an EQE of 31.39% and a power efficiency of 121.50 lm W−1, respectively. The 1D grating and 2D patterned ITO microstructures have been successfully fabricated with the holographic lithography. The phosphorescent OLEDs employing the periodic patterned ITO/glass substrate improve the light out-coupling leading to signigicantly increased light-emitting efficiency. A power efficiency of 121.50 lm W−1 is achieved for yellow phosphorescent OLEDs employing the 2D hole-patterned ITO/glass substrate. Image 1 • The 1D and 2D patterned ITO/glass substrate via holographic lithography enhances the outcoupling of emitted light from the device structure. • The light-emitting efficiencies are greatly increased by using the patterned ITO/glass substrate. • A power efficiency of 121.50 lm W−1 and an external quantum efficiency of 31.39% are achieved for yellow phosphorescent OLEDs employing the 2D hole-patterned ITO/glass substrate. [ABSTRACT FROM AUTHOR]