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Abstract: We investigate the electroluminescent performance of single-layer polymer light-emitting diodes with the emissive layer comprised of poly(N-vinyl carbazole) (PVK): electron-transporting molecules (ETMs):iridium(III) [bis(4,6-difluorophenyl)-pyridinato-N,C2]-picolinate (FIrpic) trinary components. A series of ETMs with comparable energy levels is tentatively utilized to modulate the morphology. The morphology of the emissive layer is studied using the transmission electron microscopy and atomic force microscopy in combination with the interfacial energy calculation between these components, with purpose to understand the multi-component miscibility and morphological properties of these emissive layers. It is found that the multi-component miscibility has dramatic influence on the morphology of the multi-component emissive layer and the final electroluminescent performance of the devices. The results reveal that the aggregation of ETMs mainly results in an increase of driving voltages, while the aggregation of FIrpic emitters would lead to the reduction in the luminous efficiencies as a result of their self-quenching effects. The PVK:1,3-bis[(p-tert-butyl)phenyl-1,3,4-oxadiazoyl]benzene (OXD-7): FIrpic blend demonstrates a more uniform morphology resulting in an optimal luminous efficiency of 15cdA−1. [Copyright &y& Elsevier]

Abstract: Cross-linkable polycarbazole copolymers have been synthesized starting from 3,6-diiodo-9-(2-ethylhexyl)carbazole and 3,6-diodo-9-[6-(3-ethyloxetan-3-ylmethoxy)hexyl]carbazole monomers in a Ni(0)-catalyzed Yamamoto-type aryl–aryl coupling. The synthesized materials were characterized by various techniques including differential scanning calorimetry, thermogravimetry and cyclic voltammetry. Insoluble layers of the copolymers have been obtained by photo-crosslinking thin films of the materials. Organic light emitting diodes using the crosslinked polycarbazole networks as hole transporting layer demonstrated a turn-on voltage of ca. 4V, a maximum brightness of 15,000cd/m2, and maximum OLED efficiency of 8.5cd/A. [Copyright &y& Elsevier]

Abstract: We present the results of a systematic study on how the solvent processing affects the EL properties of a single emissive layer white PLED based on a polyfluorene derivative polymer. The EL spectrum of the device using solvent processing, peaked at 436, 572nm, shows a pure white emission and the luminous efficiency is enhanced, which is attributed to the presence of the crystalline polyfluorene induced by solvent processing. The crystalline polyfluorene that acts as the self-dopant enhances the blue emission and increases the purity of the white light. Most importantly, the charge transport is balanced after solvent processing, which favors improving the luminous efficiency. A light-emitting efficiency of 12cd/A is achieved after solvent processing, about 50% increase compared to the as-spincoated device. [Copyright &y& Elsevier]

Abstract: We developed an approach to realize blue, green and red emission from top-emitting white organic light-emitting diodes (OLEDs) through depositing exterior tunable optical films on top of the OLEDs. Three primary colors for full color display including blue, green and red emission are achieved by controlling the wavelength-dependent transmittance of the multilayer optical films overlaid on the emissive layer. The advantage of such a device configuration is that the emissive color of the OLEDs can be tuned via the exterior optical films which do not affect the electrical characteristics of the device. This may provide a way to realize full color display by using white top-emitting OLEDs. [Copyright &y& Elsevier]

It is important to arrange the donor and acceptor phases and molecules within those phases in a way that optimizes relevant optoelectronic processes required for efficient operation of bulk-heterojunction (BHJ) organic solar cells (OSCs). 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) tends to adopt edge-on orientation with respect to PEDOT/PSS substrate, which is adverse to charge and exciton transport in the vertical direction. Besides, [6,6]-phenyl-C71-butyric acid methyl ester (PC 70 BM) tends to deposit on PEDOT/PSS substrate, while p -DTS(FBTTh 2) 2 is inclined to accumulate at surface, which blocks charge transport and increases injection barrier of charge. Here, we tried to optimize both the molecular orientation and vertical phase separation of p -DTS(FBTTh 2) 2 /PC 70 BM with proper crystal size and bicontinuous network structure. Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate], (PTB7-Th) was used as the interfacial layer to induce p -DTS(FBTTh 2) 2 to adopt face-on orientation because of epitaxial crystallization. At the same time, vertical phase separation can be improved due to that p -DTS(FBTTh 2) 2 tends to deposit on PTB7-Th. Consequently, the efficiency of exciton separation of devices with PTB7-Th as the interfacial layer is improved and both the hole and electron mobility were increased and became more balanced. As a result, the power conversion efficiency (PCE) increased from 5.47% to 6.74%. Image 1026 • PTB7-Th was used as the interfacial layer. • p -DTS(FBTTh 2) 2 was induced to adopt face-on orientation because of epitaxial crystallization. • Vertical phase separation of active layer was improved due to that p -DTS(FBTTh 2) 2 tends to deposit on PTB7-Th. • The efficiency of exciton separation was improved. • Both the hole and electron mobility were increased and became more balanced. [ABSTRACT FROM AUTHOR]

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]

Cheap conjugated polymer PCDTBT and its derivatives are rarely used in high-efficiency non-fullerene acceptor (NFA) organic solar cells (OSCs) due to their poor charge transport property. Herein, solid solution strategy is employed to boost the photovoltaic performance of PCDTBT:NFA-based OSCs. The PCDTBT-OR:PC 71 BM solid solution is formed when a small amount of PC 71 BM molecules are dispersed within amorphous PCDTBT-OR matrix due to their thermodynamic miscibility, which demonstrates increased hole mobility with comparison to the neat PCDTBT-OR. The hole mobility of ternary PCDTBT-OR:PC 71 BM:Y6 blend containing a small amount of PC 71 BM is also increased significantly due to the PCDTBT-OR:PC 71 BM solid solution effect. The ternary PCDTBT-OR:PC 71 BM:Y6 blend shows better charge extraction, less bimolecular recombination as well as more efficient charge transfer. Finally, the PCDTBT-OR:PC 71 BM:Y6 OSCs achieve a power conversion efficiency (PCE) of 8.42%, much higher than 6.82% of the binary PCDTBT-OR:Y6 OSCs, and it is also one of the highest values for PCDTBT:NFA-based OSCs. This work demonstrates that the cheap polymer donor PCDTBT derivatives have potential to achieve high PCE in combination with NFAs. Solid solution effect of PCDTBT-OR:PC 71 BM blend is favorable to enhance hole mobility of donor phase and renders the PCDTBT-OR:Y6-based organic solar cells (OSCs) an optimized PCE of 8.42%, which is one of the highest values for the PCDTBT:NFAs based OSCs. [Display omitted] • Solid solution effect is utilized to improve the photovoltaic performance of PCDTBT-OR:NFA OSCs. • PC 71 BM molecules tend to disperse in PCDTBT-OR matrix to form solid solutions. • Solid solution effect is favorable to improve hole transport in PCDTBT-OR:PC 71 BM blend film. • Solid solution effect enhances the hole mobility and suppresses bimolecular recombination in the ternary blend. • The optimized device achieves a PCE of 8.42%, which is one of the highest values for the PCDTBT:NFA based OSCs. [ABSTRACT FROM AUTHOR]

The exploitation of soluble and efficient deep-red phosphorescent emitters is of paramount importance for solution-processed organic light-emitting diodes (OLEDs) applied in both high-quality RGB displays and high color-rendering-index (CRI) solid-state lighting source. In this work, a new deep-red heteroleptic iridium(III) complex, i.e. bis[2,5-di(4-hexylthiophen-2-yl)pyridine][acetylacetonate]iridium(III) [Ir(ht-5ht-py) 2 (acac)], has been synthesized and successfully used to fabricate solution-processed saturated red and white organic light-emitting diodes (WOLEDs). The long alkyl side-chains of Ir(ht-5ht-py) 2 (acac) render its excellent solubility in common organic solvents and good compatibility with common host materials. The solution-processed red OLED based on Ir(ht-5ht-py) 2 (acac) exhibited a decent external quantum efficiency of 8.2% and a power efficiency of 6.5 lm/W, with satisfactory Commission International de L’Eclairage (CIE) coordinates of (0.68, 0.31) for saturated red emission. Furthermore, the prepared multiple-phosphors-doped WOLED with Ir(ht-5ht-py) 2 (acac) as the red emitter showed an excellent high color rendering index (CRI) value of 89 as well as low color-correlated temperature (CCT) of 2331 K, which can meet the call for physiologically-friendly indoor illumination. [ABSTRACT FROM AUTHOR]

A singly-linked perylene bisimide dimer (di-PBI) and a low band gap polymer based on dithienocarbazole and isoindigo moieties (P(IID-DTC)) are selected as electron acceptor and donor respectively to fabricate non-fullerene based polymer solar cells. The combination of di-PBI acceptor and P(IID-DTC) donor provides well overlapped absorption profile with solar light in the visible region. The P(IID-DTC):di-PBI blend morphology and its effect on charge transport and recombination have been investigated in detail. The dominant bimolecular recombination in commonly processed P(IID-DTC):di-PBI blend results in a low power conversion efficiency of merely 1%. We find that CH 2 Cl 2 vapor annealing can effectively improve bi-continuous phase separation and boost the electron transport by more than two orders of magnitude due to the detrap of di-PBI molecules from amorphous P(IID-DTC) matrix. More importantly, the dominant bimolecular recombination in the P(IID-DTC):di-PBI blend films is strongly suppressed. Finally, the power conversion efficiency of non-fullerene P(IID-DTC):di-PBI blend solar cell is dramatically improved to 2.95%. [ABSTRACT FROM AUTHOR]

Highlights: [•] Phase separation in solution-processed OLEDs is restrained by adjusting processing solvent. [•] The solution-processed emissive layer is denser than the vacuum-evaporated counterpart. [•] Efficient solution-processed blue OLEDs with halogen-free solvent are achieved with power efficiency of 15.6lm/W. [Copyright &y& Elsevier]

The reported NiO x interfacial layers in blue perovskite light-emitting diodes (PeLEDs) usually require high-temperature annealing and complex interface modification. Herein, we report a kind of uniform NiO x anode interfacial layer induced by H 2 O treatment, which effectively enhances the brightness and light-emitting efficiency of blue PeLEDs simultaneously. Compared to the as-prepared NiO x anode interfacial layer, H 2 O treatment renders uniform and pinhole-free NiO x morphology. The solution-processed perovskite blue emissive layer prepared atop the H 2 O-treated NiO x interfacial layer demonstrates enhanced photoluminescent property and superior morphology with low trap density. The blue PeLEDs employing H 2 O-treated NiO x as anode interfacial layer show a maximum luminance of 9052 cd/m2 and a maximum external quantum efficiency (EQE) of 1.80%, whereas the control device based on the as-prepared NiO x anode interfacial layer merely exhibits a maximum luminance of 3850 cd/m2 and an EQE of 0.88%, leading to about 135% and 104% increase in brightness and efficiency, respectively. The PeLEDs emit pure blue light with emission peak located at 482 nm and demonstrate superior spectral stability under different driving voltages and operating time. [Display omitted] • High-brightness blue PeLEDs were fabricated using NiO x interfacial layer. • H 2 O-treated NiO x interfacial layer induces to form high-quality blue perovskite emissive layer. • The blue PeLEDs attain a maximum luminance of 9052 cd/m2 and a maximum EQE of 1.80%. • The PeLEDs emit stable blue light with emission peak at 482 nm. [ABSTRACT FROM AUTHOR]

Abstract: Polyoctylfluorene thin films were made using novel solvent vapor assisted spin-coating method, which adds solvent into spin-coater and seal it for several minutes before spin-coating to form a solvent vapor atmosphere. The absorption, photoluminescence spectra, electroluminescence spectra and X-ray diffraction patterns demonstrate that β phase directly generate in such thin film while the thin film made by using normal method is amorphous, which means such method combines normal spin-coating and solvent vapor annealing together into one simply and fast process. The brightness and efficiency of related electroluminescence device are also enhanced due to the self-dopant effect. [Copyright &y& Elsevier]

Abstract: The effect of solvent mixtures on the morphologies of poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM) blend films is investigated. 1,2,4-Trichlorobenzene (TCB) which is a good solvent for PCDTBT is selected to mix with chloroform (CF), chlorobenzene (CB) and o-dichlorobenzene (oDCB) for tuning the morphology of the PCDTBT:PC71BM blend. It is found that formation of nanoscale phase separation with a fibrillar PCDTBT nanostructure of PCDTBT:PC71BM blend which is favorable for exciton separation and charge carrier transport is strongly dependent on the solubility parameters of the solvent mixtures. A clearly defined nanoscale phase separation of the PCDTBT:PC71BM blend can be obtained with TCB:CF mixture. The resulted morphology is similar to that produced with sole DCB solvent that is currently the best solvent for PCDTBT:PC71BM blend solar cells. Moreover, the TCB:CF mixture demonstrates better solubility and processibility for PCDTBT:PC71BM blend and allows us to prepare thick active layer that is required in large-area roll-to-roll process. The polymer solar cells with 250nm- thick active layer are fabricated by using TCB:CF solvent mixture and the power conversion efficiency of the devices reaches 6.45%. A highest short-circuit current of 13.6mA/cm2 is achieved due to enhanced optical absorption of thick active layer. [Copyright &y& Elsevier]

Abstract: PFO thin films made of toluene solution dissolved for 12, 30 and 80min at 55°C were prepared and then treated by solvent vapor annealing or thermal annealing. Their absorption, photoluminescence, electroluminescence and morphology were characterized. The results show that the thin film made of solution dissolved for short time contains trace β phase PFO that lead to unusual emission. After solvent vapor annealing or thermal annealing, luminescence of such thin film is lower than that made of solution dissolved for long time. The surface morphology shows that such thin film contains large aggregations with size of 120×80nm, which is in line with the light scattering results of 120nm large particles in the solution, indicating the difference of luminescence originate from the residue aggregations. Such aggregations will lead to stronger diffraction peak in the in-plane GIXRD and weaker diffraction peak in the out-of-plane GIXRD, which indicates they have more ordered structure in main chain direction that will hinder the formation of ordered packing of PFO molecular chains in out-of-plane direction. These results demonstrate that the PFO solution needs to be dissolved for enough time to realize repeatment of high quality light-emitting device for actual massive application. [Copyright &y& Elsevier]

Abstract: Enhanced performances of hybrid polymer solar cells based on a blend of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and p-methoxybenzoic acid (MBA) modified zinc oxide (ZnO) nanoparticles were reported. Both the short-circuit current and open-circuit voltage of solar cells were improved by using MBA modified ZnO nanoparticles as electron acceptor. The overall power conversion efficiency was increased from 1.09% to 1.52% under AM 1.5G 100mW/cm2 illumination after ZnO was modified with MBA at 0.1wt.%. It was found that modification of ZnO with 0.1wt.% of MBA did not affect electron and hole transport properties of the active layer. However, a fine phase separation between MEH-PPV donor and MBA-modified ZnO acceptor was obtained. The fine phase separation enhanced the exciton dissociation efficiency and hence the power conversion efficiency of solar cells. [Copyright &y& Elsevier]

Abstract: A kind of tandem polymer photovoltaic cell with inorganic metal oxides as a transparent middle connection unit to link the two subcells having different absorption characteristics is developed and its open-circuit voltage origin is investigated. The middle connection unit consists of an electron-transporting titanium oxide (TiO x ) layer, a thin aluminum (Al) layer and a hole-transporting molybdenum oxide (MoO3) layer. The inserted thin Al layer between the TiO x and MoO3 layers not only acts as an efficient recombination site for electrons and holes photo-generated in the two subcells, but also realigns the electronic energy levels at TiO x /MoO3 interfaces to reduce the open-circuit voltage loss. The open-circuit voltage of the tandem cell is the summation of the two subcells. [Copyright &y& Elsevier]

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]

Abstract: Tandem polymer photovoltaic cells with the subcells having different absorption characteristics in series connection are widely investigated to enhance absorption coverage over the solar spectrum. Herein, we demonstrate efficient tandem polymer photovoltaic cells with the two stacked subcells comprising different band-gap conjugated polymer and fullerene derivative bulk heterojunction in parallel connection. A semitransparent metal layer combined with inorganic semiconductor compounds is utilized as the intermediate electrode of the two stacked subcells to create the required built-in potential for collecting photo-generated charges. The short-circuit current of the stacked cell is the sum of the subcells and the open-circuit voltage is similar to the subcells. [Copyright &y& Elsevier]

The reported semi-transparent organic solar cells (ST-OSCs) are commonly based on a middle bandgap donor and narrow bandgap acceptor blend, for example, the PTB7-Th:Y6 blend. However, the strong absorption of PTB7-Th in the visible region hinders the further improvement of average visible transmission (AVT) for the ST-OSCs. Here we report a new kind of all-small-molecule ST-OSCs based on TAPC:Y6 blend. The used donor TAPC has little absorption in the visible region, which is beneficial for attaining high transparency. The optimized ST-OSCs based on TAPC:Y6 blend realize a power conversion efficiency of 3.01%. Importantly, a high AVT of 47.99% is achieved for this kind of ST-OSCs, much higher than those of reported ST-OSCs. The proposed TAPC:Y6 ST-OSCs also have a good color perception, whose CIE 1931 coordinates are (0.292,0.313) and color rendering index is 94.5. [Display omitted] • Transparent wide-bandgap donor is used to fabricate highly transparent OSCs. • Average visible transmission of 84.92% for TAPC:Y6 blend film and 47.99% for the device are obtained. • The semi-transparent OSCs attain an power conversion efficiency of 3.01%. • The semi-transparent OSCs show superior color perception and color rendering index. [ABSTRACT FROM AUTHOR]

Nonfullerene acceptors are currently dominating the research and development of organic photovoltaics (OPVs). Exploring the charge separation mechanism is helpful to understand the photovoltaic process in efficient nonfullerene-based OPVs. Herein, we have selected two typical acceptors: PC 71 BM and nonfullerene acceptor IT-M, and have studied the device function and the ultrafast charge carrier dynamics in the PBDB-TF:IT-M and PBDB-TF:PC 71 BM blends to investigate how they are affected by different blend morphologies induced by using a popular solvent additive 1,8-diiodooctane (DIO). It is found that ultrafast charge generation occurs in both of the two blend systems. For the IT-M blend film, the DIO additive strongly affects the ultrafast photophysical process. Efficient hole transfer is observed for the IT-M blend processed with DIO compared to the pristine IT-M blend. Moreover, the charge density is significantly increased in the DIO-processed IT-M blend film. In contrast to the IT-M blend, the DIO does not strongly affect the ultrafast charge carrier dynamics in PC 71 BM blend possibly due to its slight effect on the blend morphology. The reionization of spin-triplet charge transfer states can occur faster than relaxation to triplet in both of the well-ordered blend film processed with DIO resulting in an enhanced current density and fill factor. Image 1 • Ultrafast charge separation is observed in both PBDB-TF:IT-M and PBDB-TF:PC 71 BM blend films. • Efficient hole transfer occurs and the charge density is significantly increased in DIO-processed PBDB-TF:IT-M blend film. • The reionization of 3CT states can occur faster than relaxation to triplet excitons in both fullerene and nonfullerene blend films processed with DIO. [ABSTRACT FROM AUTHOR]

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]