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A simple approach to fabricate high-efficiency annealing-free poly(3-hexylthiophene): [6,6]-phenyl C(61)-butyric acid methyl ester (P3HT:PCBM) solar cells is reported by using p-type CuI to substitute PEDOT:PSS as anode buffer layer. It is found that the P3HT:PCBM blend films deposited on CuI surface show different orientation of crystalline P3HT domains and phase separation from those deposited on PEDOT:PSS surface. A nanoscale phase separation of P3HT and PCBM with domain sizes about 10-30 nm is formed for the P3HT:PCBM blend films deposited on CuI surface. Absorption and grazing incidence X-ray diffraction (GIXRD) experiments indicate that the CuI layer not only induces the self-organization of P3HT chains into well-ordered structure but also results in the vertical orientation of π-π stacking planes of P3HT with respect to the substrate which is favorable for the hole collection in polymer solar cells. Hole-transport investigation discloses that hole mobility of the as-spincast P3HT:PCBM blend film on CuI surface is increased with 3 orders of magnitude compared to the P3HT:PCBM film deposited on PEDOT:PSS. A power conversion efficiency of 3.1% for the as-spincast P3HT:PCBM solar cell with CuI buffer layer is about 4-fold enhancement compared to 0.83% of the control device with PEDOT:PSS, and is comparable to the reported P3HT:PCBM solar cells subjected to post thermal treatments. This work implies that interfacial engineering is a promising approach for manipulating morphology of active layer and can potentially simplify the process and shorten the fabrication time of polymer solar cells in low-cost roll-to-roll manufacturing.

Two new wide bandgaps D−A copolymers compromising of same benzo [1,2‐b:4, 5‐b′]dithiophene functionalized with thiazole side‐chain donor unit and different acceptors units, i. e., fluorinated benzotriazole (FBTA) (PBDTTZ‐FBTA) and bis‐thiophene‐thieno‐benzothiazole (BTZ) (PBDTTZ‐BTZ) were synthesized and their optical and electrochemical properties were investigated. These copolymers exhibit appropriate frontier energy levels and complementary absorption to most middle and narrow bandgap non‐fullerene small molecule non‐fullerene acceptors. We have explored using these two copolymers as donors combined with a narrow bandgap non‐fullerene acceptor, namely BThIND−Cl, for the construction of polymer solar cells. The optimized polymer solar cells employing PBDTTZ‐FBTA: BThIND−Cl showed overall power conversion efficiency of 14.96 % (with energy loss of 0.51 eV), which is higher than that for PBDTTZ‐BTZ: BThIND−Cl (11.68 % with energy loss of 0.56 eV). Although the PBDTTZ‐BTZ exhibits a broader absorption profile than that of PBDTTZ‐FBTA, the higher power conversion efficiency of the later copolymer may be correlated with the high charge carrier mobility, suppression of the bimolecular and trap‐assisted recombination due to appropriate phase separation and compact π‐π stacking distance in the active layer and low energy loss. [ABSTRACT FROM AUTHOR]

To examine the effects of pendent alkyl chain on the benzodithiophenedione (BDD) acceptor in the donor–acceptor (D–A) conjugated copolymers, two D–A copolymers with same thiazole ring substituted benzo[1,2‐b:4,5‐b′]dithiophene (BDTTz) and different acceptors BDD with two pendent alkyl units PBDTTz‐BDD and one pendent alkyl unit in benzo[1,2‐b:4,5‐c′]dithiophene‐4,8‐dione (BDTD) PBDTTz‐BDTD are synthesized. There is small effect on the optical properties but significant effect on the intermolecular π–π stacking, charge transport, and photovoltaic performance. PBTTz‐BDTD (with one pendent alkyl chain) on the BDD exhibits smaller π–π stacking distance as compared to PBDTTz‐BDD (with two pendent alkyl chains). The balanced charge carrier mobilities for the PBDTTZ‐BDTD based blends than those for PBDTTz‐BDD based blends are beneficial for suppressing the recombination processes, resulting in higher short circuit current and fill factor for the polymer solar cells (PSCs) based on PBDTTz‐BDTD. Combined with BThIND or Y6 as acceptor, PBDTTZ‐BDTD based PSCs show power conversion efficiency of 12.85% and 14.08%, respectively, which are larger than that for PBDTTz‐BDD counterparts (10.46% and 10.90% for BThIND and Y6, respectively). Thus, the photovoltaic performance of the D–A copolymer donors can be regulated through the slight variations of the pendent alkyl chains in the BDD acceptor unit. [ABSTRACT FROM AUTHOR]

In this work, two D−A conjugated polymers having same fluorinated benzothiadiazole acceptor and thiophene linker and different donor units (2,8‐dibromo‐4,6‐bis9n‐octylthiophene‐2‐yl)benzo(2,1‐b:3,4‐b':5,6‐c"] trithiophene for P95 and 5,8‐dibromo‐2‐[5‐2(‐ethylhexyl)thiophene‐2yl]‐1H bisthieno[3,2‐e:2',3'‐g]benzothiazole for P96 were synthesized. These polymers have complementary absorption spectra with both phenyl C71 butyric acid methyl ester (PC71BM) and non‐fullerene acceptor (PDIF) and energy levels for the exciton dissociation and charge transfer. After the optimization, the P95:PDIF and P96:PDIF based polymer solar cells showed overall PCE of showed 9.40% and 9.18% with energy loss of 0.54 eV and 0.64 eV, respectively which is higher than that of PC71BM counterpart (8.34% and 7.82% for P95 and P96, respectively). The higher values of short circuit current (Jsc) and open circuit voltage (Voc) and related to strong absorption of PDIF in 400–600 nm wavelength region and shallow value of lowest unoccupied molecular orbital (LUMO) energy level of PDIF. The higher value of power conversion efficiency of polymer solar cells based on P95, for both PC71BM and PDIF is related to the broader absorption spectra of P95 (low optical bandgap) as compared to P96 and more balanced charge transport due to higher hole mobility for P95 based active layer. These results demonstrate that the electron donating ability of donor unit in the D−A conjugated polymers may affect the photovoltaic response of the polymer solar cells and provide the guidance for the design of high efficiency photovoltaic materials. [ABSTRACT FROM AUTHOR]

A series of novel donor–acceptor (D–A) random conjugated terpolymers P2‐P4 along with the homopolymers P1 (BDT‐DPP) and P5 (BDT‐BTDQ) were designed and synthesized by copolymerizing a benzo[1,2‐b:4,5‐b]dithiophene (BDT) donor with an electron‐deficient diketopyrrolo[3,4‐c]pyrrole (DPP) unit and a benzothiadiazolo[3,4‐e]quinoxaline (BTDQ) moieties of different electron‐withdrawing strengths, and the resultant terpolymers showed broad absorption profile ranging from 300 to 1200 nm. The HOMO levels of the polymers were adjusted from −5.23 to −5.11 eV, and the optical bandgaps were controlled from 1.32 to 1.13 eV by changing the molar ratio of DPP and BTDQ acceptors. These terpolymers were used as a donor along with PC71BM as an acceptor for the creation of polymer solar cells, and the performance was optimized via variable the donor to acceptor ratio and solvent vapor annealing. The polymer solar cells made from the random terpolymer P3 showed the highest overall power conversion efficiency of (9.27%), which is higher than that for the corresponding homo‐polymers counterparts, that is, P1 (7.27%) and P5 (7.68%). The results demonstrate that the designing of random D‐A1‐D‐A2 terpolymers may be the best approach for efficient polymer solar cells. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1478–1485 [ABSTRACT FROM AUTHOR]

For polymer solar cells (PSCs) with conventional configuration, the vertical composition profile of donor:acceptor in active layer is detrimental for charge carrier transporting/collection and leads to decreased device performance. A cross-linkable donor polymer as the underlying morphology-inducing layer (MIL) to tune the vertical composition distribution of donor:acceptor in the active layer for improved PSC device performance is reported. With poly(thieno[3,4- b]-thiophene/benzodithiophene):[6,6]-phenyl C71-butyric acid methyl ester (PTB7:PC71BM) as the active layer, the MIL material, PTB7-TV, is developed by attaching cross-linkable vinyl groups to the side chain of PTB7. PSC device with PTB7-TV layer exhibits a power conversion efficiency (PCE) of 8.55% and short-circuit current density ( JSC) of 15.75 mA cm−2, in comparison to PCE of 7.41% and JSC of 13.73 mA cm−2 of the controlled device. The enhanced device performance is ascribed to the much improved vertical composition profile and reduced phase separation domain size in the active layer. These results demonstrate that cross-linked MIL is an effective strategy to improve photovoltaic performance of conventional PSC devices. [ABSTRACT FROM AUTHOR]

The article examines the solvent vapor annealing effect of poly(3-hexylthiophene) (P3HT)/methanofullerene (PCBM) blend on its morphology and optoelectronic properties. It notes the effect of the organic solvents of choice for the treatment on the morphology of P3HT/PCBM blend and the device performance. The solvent used vapor treatment should reportedly have good solubility to both P3HT and PCBM. Solvent vapor treatment and post-thermal annealing enable high power conversion efficiency (PCE).

New donor/acceptor polymers PBDTDPT1and PBDTDPT2with alternating benzodithiophene and N-alkylated dioxopyrrolo-thiophene were synthesized. The new polymers had deep HOMO levels of −5.42 and −5.44 eV for PBDTDPT1and PBDTDPT2, respectively. A PBDTDPT2based BHJ solar cell device achieved a PCE of 4.79% and Vocof 0.91 V. [ABSTRACT FROM AUTHOR]

Abstract: New donor/acceptor polymers PBDTTPT1 and PBDTTPT2 with alternating benzodithiophene (BDT) and bisthiophene-dioxopyrrolothiophene (TPT) units were synthesized by Stille coupling reaction. The polymers had optical bandgaps of 1.78 and 1.82 eV, and HOMO energy levels of −5.30 and −5.35 eV for PBDTTPT1 and PBDTTPT2, respectively. Polymeric solar cell devices based on these copolymers as donors and PC71BM as acceptor showed the highest open circuit voltage of 0.95 V and power conversion efficiency of 2.68% under the illumination of AM 1.5, 100 mW/cm2. [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]

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]

Abstract: A series of novel donor–acceptor (D–A) liquid crystalline conjugated cooligomers, i.e. F3T4-epP, F4T6-epP and F5T8-epP, which comprise oligo(fluorene-alt-bithiophene)s (OFbTs) with the different lengths as the donor segments and a perylene diimide (PDI) derivative as the acceptor segment, were designed and synthesized. The cooligomers can form the films with the desired ideal morphology for bulk heterojunction (BHJ) polymer solar cells (PSCs). That means the films comprise ordered alternating D–A lamellae perpendicular to the substrates. Most importantly, the periods of the nanostructures can be tuned by varying molecular length and post-treatment condition. For F3T4-epP and F4T6-epP, the periods are close to the single and double molecular lengths upon thermal and solvent vapor annealing, respectively. However, only the nanostructures with the period close to the single molecular length were formed for F5T8-epP for both annealing processes. Solar cells based on above nanostructured films were fabricated to demonstrate the advantages of the ideal morphology for BHJ solar cells. It was found that the power conversion efficiency (PCE) of the devices was dependent on the molecular length and the order of the films. Solvent vapor annealed films exhibited the highest order therefore gave the best device performance. A PCE of 1.75% was demonstrated with the solvent vapor annealed films of F5T8-epP. This performance represents the best among the solar cells based on the single molecular materials. [Copyright &y& Elsevier]