Benzobisthiazole as Weak Donor for Improved Photovoltaic Performance: Microwave Conductivity Technique Assisted Molecular Engineering

New donor–acceptor‐type copolymers comprised of benzobisthiazole (BBTz) as a weak donor rather than acceptor are proposed. This approach can simultaneously lead to deepening the HOMO and LUMO of the polymers with moderate energy offset against fullerene derivatives in bulk heterojunction organic photovoltaics. As a proof‐of‐concept, BBTz‐based random copolymers conjugated with typical electron acceptors: thienopyrroledione (TPD) and benzothiadiazole (BT) based on density functional theory calculations are synthesized. Laser‐flash and Xe‐flash time‐resolved microwave conductivity (TRMC) evaluations of polymer:[6,6]‐phenyl C₆₁ butyric acid methyl ester (PCBM) blends are conducted to screen the feasibility of the copolymers, leading to optimization of processing conditions for photovoltaic device application. According to the TMRC results, alternating BBTz‐BT copolymers are designed, exhibiting extended photoabsorption up to ca. 750 nm, deep HOMO (–5.5 to –5.7 eV), good miscibility with PCBM, and inherent crystalline nature. Moreover, the maximized PCE of 3.8%, the top‐class among BBTz‐based polymers reported so far, is realized in an inverted cell using TiO_x and MoO_x as the buffer layers. This study opens up opportunities to create low‐bandgap polymers with deep HOMO, and shows how the device‐less TRMC evaluation is of help for decision‐making on judicious molecular design.     

Donor and Acceptor Unit Sequences Influence Material Performance in Benzo[1,2‐b:4,5‐b′]dithiophene–6,7‐Difluoroquinoxaline Small Molecule Donors for BHJ Solar Cells

Well‐defined small molecule (SM) donors can be used as alternatives to π‐conjugated polymers in bulk‐heterojunction (BHJ) solar cells with fullerene acceptors (e.g., PC₆₁/₇₁BM). Taking advantage of their synthetic tunability, combinations of various donor and acceptor motifs can lead to a wide range of optical, electronic, and self‐assembling properties that, in turn, may impact material performance in BHJ solar cells. In this report, it is shown that changing the sequence of donor and acceptor units along the π‐extended backbone of benzo[1,2‐b:4,5‐b′]dithiophene–6,7‐difluoroquinoxaline SM donors critically impacts (i) molecular packing, (ii) propensity to order and preferential aggregate orientations in thin‐films, and (iii) charge transport in BHJ solar cells. In these systems ( SM1‐3 ), it is found that 6,7‐difluoroquinoxaline ([2F]Q) motifs directly appended to the central benzo[1,2‐b:4,5‐b′]dithiophene (BDT) unit yield a lower‐bandgap analogue ( SM1 ) with favorable molecular packing and aggregation patterns in thin films, and optimized BHJ solar cell efficiencies of ≈6.6%. ¹H‐¹H DQ‐SQ NMR analyses indicate that SM1 and its counterpart with [2F]Q motifs substituted as end‐group SM3 possess distinct self‐assembly patterns, correlating with the significant charge transport and BHJ device efficiency differences observed for the two analogous SM donors (avg. 6.3% vs 2.0%, respectively).     

Effect of Alkyl Side‐Chain Length on Photovoltaic Properties of Poly(3‐alkylthiophene)/PCBM Bulk Heterojunctions

The morphological, bipolar charge‐carrier transport, and photovoltaic characteristics of poly(3‐alkylthiophene) (P3AT):[6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) blends are studied as a function of alkyl side‐chain length m, where m equals the number of alkyl carbon atoms. The P3ATs studied are poly(3‐butylthiophene) (P3BT, m = 4), poly(3‐pentylthiophene) (P3PT, m = 5), and poly(3‐hexylthiophene) (P3HT, m = 6). Solar cells with these blends deliver similar order of photo‐current yield (exceeding 10 mA cm^?2) irrespective of side‐chain length. Power conversion efficiencies of 3.2, 4.3, and 4.6% are within reach using solar cells with active layers of P3BT:PCBM (1:0.8), P3PT:PCBM (1:1), and P3HT:PCBM (1:1), respectively. A difference in fill factor values is found to be the main source of efficiency difference. Morphological studies reveal an increase in the degree of phase separation with increasing alkyl chain length. Moreover, while P3PT:PCBM and P3HT:PCBM films have similar hole mobility, measured by hole‐only diodes, the hole mobility in P3BT:PCBM lowers by nearly a factor of four. Bipolar measurements made by field‐effect transistor showed a decrease in the hole mobility and an increase in the electron mobility with increasing alkyl chain length. Balanced charge transport is only achieved in the P3HT:PCBM blend. This, together with better processing properties, explains the superior properties of P3HT as a solar cell material. P3PT is proved to be a potentially competitive material. The optoelectronic and charge transport properties observed in the different P3AT:PCBM bulk heterojunction (BHJ) blends provide useful information for understanding the physics of BHJ films and the working principles of the corresponding solar cells.     

Silaindacenodithiophene‐Based Low Band Gap Polymers – The Effect of Fluorine Substitution on Device Performances and Film Morphologies

Silaindacenodithiophene is copolymerized with benzo[c][1,2,5]thiadiazole ( BT ) and 4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole ( DTBT ), respectively their fluorinated counter parts 5,6‐difluorobenzo[c][1,2,5]thiadiazole ( 2FBT ) and 5,6‐difluoro‐4,7‐di(thiophen‐2‐yl) benzo[c][1,2,5]thiadiazole ( 2FDTBT ). The influence of the thienyl spacers and fluorine atoms on molecular packing and active layer morphology is investigated with regard to device performances. bulk heterojunction (BHJ) solar cells based on silaindacenodithiophene donor‐acceptor polymers achieved PCE's of 4.5% and hole mobilities of as high as 0.28 cm²/(V s) are achieved in an organic field‐effect transistor (OFET).     

Charge‐Transport Properties of F6TNAP‐Based Charge‐Transfer Cocrystals

The crystal structures of the charge‐transfer (CT) cocrystals formed by the π‐electron acceptor 1,3,4,5,7,8‐hexafluoro‐11,11,12,12‐tetracyanonaphtho‐2,6‐quinodimethane (F₆TNAP) with the planar π‐electron‐donor molecules triphenylene (TP), benzo[b]benzo[4,5]thieno[2,3‐d]thiophene (BTBT), benzo[1,2‐b:4,5‐b′]dithiophene (BDT), pyrene (PY), anthracene (ANT), and carbazole (CBZ) have been determined using single‐crystal X‐ray diffraction (SCXRD), along with those of two polymorphs of F₆TNAP. All six cocrystals exhibit 1:1 donor/acceptor stoichiometry and adopt mixed‐stacking motifs. Cocrystals based on BTBT and CBZ π‐electron donor molecules exhibit brickwork packing, while the other four CT cocrystals show herringbone‐type crystal packing. Infrared spectroscopy, molecular geometries determined by SCXRD, and electronic structure calculations indicate that the extent of ground‐state CT in each cocrystal is small. Density functional theory calculations predict large conduction bandwidths and, consequently, low effective masses for electrons for all six CT cocrystals, while the TP‐, BDT‐, and PY‐based cocrystals are also predicted to have large valence bandwidths and low effective masses for holes. Charge‐carrier mobility values are obtained from space‐charge limited current (SCLC) measurements and field‐effect transistor measurements, with values exceeding 1 cm² V^?1 s¹ being estimated from SCLC measurements for BTBT:F₆TNAP and CBZ:F₆TNAP cocrystals.     

A Simple and Effective Modification of PCBM for Use as an Electron Acceptor in Efficient Bulk Heterojunction Solar Cells

[6,6]‐phenyl‐C‐61‐butyric acid methyl ester (PCBM) and poly(3‐hexylthiophene) (P3HT) are the most widely used acceptor and donor materials, respectively, in polymer solar cells (PSCs). However, the low LUMO (lowest unoccupied molecular orbital) energy level of PCBM limits the open circuit voltage (V_oc) of the PSCs based on P3HT. Herein a simple, low‐cost and effective approach of modifying PCBM and improving its absorption is reported which can be extended to all fullerene derivatives with an ester structure. In particular, PCBM is hydrolyzed to carboxylic acid and then converted to the corresponding carbonyl chloride. The latter is condensed with 4‐nitro‐4’‐hydroxy‐α‐cyanostilbene to afford the modified fullerene F . It is more soluble than PCBM in common organic solvents due to the increase of the organic moiety. Both solutions and thin films of F show stronger absorption than PCBM in the range of 250–900 nm. The electrochemical properties and electronic energy levels of F and PCBM are measured by cyclic voltammetry. The LUMO energy level of F is 0.25 eV higher than that of PCBM. The PSCs based on P3HT with F as an acceptor shows a higher V_oc of 0.86 V and a short circuit current (J_sc) of 8.5 mA cm^?2, resulting in a power conversion efficiency (PCE) of 4.23%, while the PSC based on P3HT:PCBM shows a PCE of about 2.93% under the same conditions. The results indicate that the modified PCBM, i.e., F , is an excellent acceptor for PSC based on bulk heterojunction active layers. A maximum overall PCE of 5.25% is achieved with the PSC based on the P3HT: F blend deposited from a mixture of solvents (chloroform/acetone) and subsequent thermal annealing at 120 °C.     

Ladder-Like Difluoroindacenodithiophene-4,9-dione Derivative: A New Acceptor System for High-Mobility n-Type Polymer Semiconductors

Ladder-like aromatic diketones (LADK), which possess a coplanar π-extended geometry, a high electron deficiency as well as various attractive optoelectronic properties, are demonstrated as the promising candidates in building small-molecule organic electron-transporting materials, yet reports on direct integration of these structural motifs into n-type polymers are rarely accessed. Herein, it is demonstrated that a possibility of realizing unipolar n-type characteristics of such acceptor system by developing two novel donor–acceptor type polymers, in which the newly developed LADK unit, named as 3,8-bis(2-decyltetradecyl)-5,10-difluoro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione (FIDTO-R), is adopted as the acceptor segments. The resulting polymers present deep-lying unoccupied molecular orbital levels (as low as −3.84 eV), compact π–π stacking (d-spacing, ≈3.57 Å) coupled with uniform nanofiber-like surface morphology. All these factors contribute to excellent unipolar n-type characteristics with high electron mobilities of 0.27 and 1.01 cm² V⁻¹ s⁻¹, together with high inverter gain values of 141 and 80, respectively. The recorded values are among the best in n-type polymer field-effect transistors and associated inverter circuits. These findings unambiguously reveal that the as-prepared FIDTO-R and its analog LADK derivatives are another type of excellent building blocks for the construction of high-mobility n-type polymers.     

Photoconductivity of a Low‐Bandgap Conjugated Polymer

The photoconductive properties of a novel low‐bandgap conjugated polymer, poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)], PCPDTBT, with an optical energy gap of E_g ～ 1.5 eV, have been studied. The results of photoluminescence and photoconductivity measurements indicate efficient electron transfer from PCPDTBT to PCBM ([6,6]‐phenyl‐C61 butyric acid methyl ester, a fullerene derivative), where PCPDTBT acts as the electron donor and PCBM as the electron acceptor. Electron‐transfer facilitates charge separation and results in prolonged carrier lifetime, as observed by fast (t > 100 ps) transient photoconductivity measurements. The photoresponsivities of PCPDTBT and PCPDTBT:PCBM are comparable to those of poly(3‐hexylthiophene), P3HT, and P3HT:PCBM, respectively. Moreover, the spectral sensitivity of PCPDTBT:PCBM extends significantly deeper into the infrared, to 900 nm, than that of P3HT. The potential of PCPDTBT as a material for high‐efficiency polymer solar cells is discussed.     

Alkoxy‐Functionalized Thienyl‐Vinylene Polymers for Field‐Effect Transistors and All‐Polymer Solar Cells

π‐conjugated polymers based on the electron‐neutral alkoxy‐functionalized thienyl‐vinylene (TVTOEt) building‐block co‐polymerized, with either BDT (benzodithiophene) or T2 (dithiophene) donor blocks, or NDI (naphthalenediimide) as an acceptor block, are synthesized and characterized. The effect of BDT and NDI substituents (alkyl vs alkoxy or linear vs branched) on the polymer performance in organic thin film transistors (OTFTs) and all‐polymer organic photovoltaic (OPV) cells is reported. Co‐monomer selection and backbone functionalization substantially modifies the polymer MO energies, thin film morphology, and charge transport properties, as indicated by electrochemistry, optical spectroscopy, X‐ray diffraction, AFM, DFT calculations, and TFT response. When polymer P7 is used as an OPV acceptor with PTB7 as a donor, the corresponding blend yields TFTs with ambipolar mobilities of μ_e = 5.1 × 10^?3 cm² V^–1 s^–1 and μ_h = 3.9 × 10^?3 cm² V^–1 s^–1 in ambient, among the highest mobilities reported to date for all‐polymer bulk heterojunction TFTs, and all‐polymer solar cells with a power conversion efficiency (PCE) of 1.70%, the highest reported PCE to date for an NDI‐polymer acceptor system. The stable transport characteristics in ambient and promising solar cell performance make NDI‐type materials promising acceptors for all‐polymer solar cell applications.     

Naphthacenodithiophene Based Polymers—New Members of the Acenodithiophene Family Exhibiting High Mobility and Power Conversion Efficiency

Wide‐bandgap conjugated polymers with a linear naphthacenodithiophene (NDT) donor unit are herein reported along with their performance in both transistor and solar cell devices. The monomer is synthesized starting from 2,6‐dihydroxynaphthalene with a double Fries rearrangement as the key step. By copolymerization with 2,1,3‐benzothiadiazole (BT) via a palladium‐catalyzed Suzuki coupling reaction, NDT‐BT co‐polymers with high molecular weights and narrow polydispersities are afforded. These novel wide‐bandgap polymers are evaluated as the semiconducting polymer in both organic field effect transistor and organic photovoltaic applications. The synthesized polymers reveal an optical bandgap in the range of 1.8 eV with an electron affinity of 3.6 eV which provides sufficient energy offset for electron transfer to PC₇₀BM acceptors. In organic field effect transistors, the synthesized polymers demonstrate high hole mobilities of around 0.4 cm² V^–1 s^–1. By using a blend of NDT‐BT with PC₇₀BM as absorber layer in organic bulk heterojunction solar cells, power conversion efficiencies of 7.5% are obtained. This value is among the highest obtained for polymers with a wider bandgap (larger than 1.7 eV), making this polymer also interesting for application in tandem or multijunction solar cells.     

Donor–acceptor copolymers based on benzo[1,2-b:4,5-b′]dithiophene and pyrene-fused phenazine for high-performance polymer solar cells

Two novel donor–acceptor (D–A)-type conjugated polymers of PTTPPz-BDT and PTTPPz-BDTT were successfully synthesized by Stille coupling polymerization, in which 7,8-dialkoxy benzo[1,2-b:4,5-b′]dithiophene (BDT) and 7,8-bithienyl benzo[1,2-b:4,5-b′]dithiophene (BDTT) were used as donor units, thiophene and pyrene-fused phenazine (PPz) were employed as π-bridges and acceptor units, respectively. High carrier mobilities, broad absorption spectra, narrow optical band gaps, and low HOMO energy levels were observed for both polymers. Furthermore, high-efficiency photovoltaic performance with power conversion efficiency (PCE) over 4.25% was exhibited in their polymer solar cells (PSCs) using [6,6]-phenyl-C₇₁-butyric-acid-methyl-ester (PC₇₁BM) as acceptor. The maximum PCE of 4.86% with short-circuit current density of 11.10 mA cm⁻² and fill factor of 62.5% was obtained in the PTTPPz-BDTT based cell. These results indicate that incorporating large planar PPz moiety into D–A-type copolymer is an efficient approach to improve photovoltaic performance for PSCs.     

Efficient bulk heterjunction solar cells based on a low-bandgap polyfluorene copolymers and fullerene derivatives

A low-bandgap polymer (PF-PThCVPTZ) consisted of fluorene and phenothiazine was designed and synthesized. With the donor–acceptor segment, the partial charge transfer can be built in the polymer backbone leading to a wide absorbance. The absorption spectrum of PF-PThCVPTZ exhibits a peak at 510 nm and an absorption onset at 645 nm in the visible range. As blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor, narrow bandgap PF-PThCVPTZ as electron donor shows significant solar cell performance. Under AM 1.5 G, 100 mA/cm² illumination, a power conversion efficiency (PCE) of 1.85% was recorded, with a short circuit current (J_SC) of 5.37 mA/cm², an open circuit voltage (V_OC) of 0.80 V, and a fill factor (FF) of 43.0%.     

High‐Performance Pseudoplanar Heterojunction Ternary Organic Solar Cells with Nonfullerene Alloyed Acceptor

The vast majority of ternary organic solar cells are obtained by simply fabricating bulk heterojunction (BHJ) active layers. Due to the inappropriate distribution of donors and acceptors in the vertical direction, a new method by fabricating pseudoplanar heterojunction (PPHJ) ternary organic solar cells is proposed to better modulate the morphology of active layer. The pseudoplanar heterojunction ternary organic solar cells (P‐ternary) are fabricated by a sequential solution treatment technique, in which the donor and acceptor mixture blends are sequentially spin‐coated. As a consequence, a higher power conversion efficiency (PCE) of 14.2% is achieved with a V_oc of 0.79 V, J_sc of 25.6 mA cm^?2, and fill factor (FF) of 69.8% compared with the ternary BHJ system of 13.8%. At the same time, the alloyed acceptor is likely formed between two the acceptors through a series of in‐depth explorations. This work suggests that nonfullerene alloyed acceptor may have great potential to realize effective P‐ternary organic solar cells.     

Effects of Postproduction Treatment on Plastic Solar Cells

Efficiencies of organic solar cells based on an interpenetrating network of a conjugated polymer and a fullerene as donor and acceptor materials still need to be improved for commercial use. We have developed a postproduction treatment that improves the performance of solar cells based on poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl C₆₁‐butyric acid methyl ester (PCBM) by means of a tempering cycle at elevated temperatures in which an external voltage is simultaneously applied, resulting in a significant increase of the short‐circuit current. Using this postproduction treatment, an enhancement of the short‐circuit current density, I_sc, to 8.5 mA cm^–2 under illumination with white light at an illumination intensity of 800 W m^–2 and an increase in external quantum efficiency (IPCE, incident photon to collected electron efficiency) to 70 % are demonstrated.     

Effect of Donor Molecular Structure and Gate Dielectric on Charge‐Transporting Characteristics for Isoindigo‐Based Donor–Acceptor Conjugated Polymers

This study investigates the effect of the molecular structure of three different donor units, naphthalene (Np), bithiophene (BT), and thiophene–vinylene–thiophene (TVT), in isoindigo (IIG)‐based donor –acceptor conjugated polymers (PIIG‐Np, PIIG‐BT and PIIG‐TVT) on the charge carrier mobility of organic field‐effect transistors (OFETs). The charge transport properties of three different IIG‐based polymers strongly depend on donor units. PIIG–BT OFETs showed 50 times higher hole mobility (0.63 cm² V^?1 s^?1) than PIIG–TVT and PIIG–Np ones of ≈ 0.01 cm² V^?1 s^?1 with CYTOP dielectric though the BT units have less planarity than the TVT and Np units. The reasons for the different mobility in IIG‐based polymers are studied by analyzing the energy structure by absorption spectra, calculating transport levels by density functional theory, investigating the in‐ and out‐of‐plane crystallinity of thin film by grazing‐incidence wide‐angle X‐ray scattering, and extracting key transport parameters via low‐temperature measurements. By combining theoretical, optical, electrical, and structural analyses, this study finds that the large difference in OFET mobility mainly originates from the transport disorders determined by the different microcrystal structure, rather than the intrinsic transport properties in isolated chains for different polymers.     

Microphase‐Separated Donor–Acceptor Diblock Copolymers: Influence of HOMO Energy Levels and Morphology on Polymer Solar Cells

The synthesis of novel semiconducting donor–acceptor (D–A) diblock copolymers by means of nitroxide‐mediated polymerization (NMP) is reported. The copolymers contain functional moieties for hole transport, electron transport, and light absorption. The first block, representing the donor, is made up of either substituted triphenylamines (poly(bis(4‐methoxyphenyl)‐4′‐vinylphenylamine), PvDMTPA) or substituted tetraphenylbenzidines (poly(N,N′‐bis(4‐methoxyphenyl)‐N‐phenyl‐N′‐4‐vinylphenyl‐(1,1′‐biphenyl)‐4,4′‐diamine), PvDMTPD). The second block consists of perylene diimide side groups attached to a polyacrylate backbone (PPerAcr) via a flexible spacer. This block is responsible for absorption in the visible range and for electron‐transport properties. The electrochemical properties of these fully functionalized diblock copolymers, PvDMTPA‐b‐PPerAcr and PvDMTPD‐b‐PPerAcr, are investigated by cyclic voltammetry (CV), and their morphology is investigated by transmission electron microscopy (TEM). All diblock copolymers exhibit microphase‐separated domains in the form of either wire‐ or wormlike structures made of perylene diimide embedded in a hole‐conductor matrix. In single‐active‐layer organic solar cells, PvDMTPD‐b‐PPerAcr reveals a fourfold improvement in power conversion efficiency (η = 0.26 %, short‐circuit current (I_SC) 1.21 mA cm^–2), and PvDMTPA‐b‐PPerAcr a fivefold increased efficiency (η = 0.32 %, I_SC = 1.14 mA cm^–2) compared with its unsubstituted analogue PvTPA‐b‐PPerAcr (η = 0.065 %, I_SC = 0.23 mA cm^–2).     

Dithienocarbazole‐Based Ladder‐Type Heptacyclic Arenes with Silicon,Carbon, and Nitrogen Bridges: Synthesis,Molecular Properties,Field‐Effect Transistors,and Photovoltaic Applications

A new class of ladder‐type dithienosilolo‐carbazole ( DTSC ), dithienopyrrolo‐carbazole ( DTPC ), and dithienocyclopenta‐carbazole ( DTCC ) units is developed in which two outer thiophene subunits are covalently fastened to the central 2,7‐carbazole cores by silicon, nitrogen, and carbon bridges, respectively. The heptacyclic multifused monomers are polymerized with the benzothiadiazole ( BT ) acceptor by palladium‐catalyzed cross‐coupling to afford three alternating donor‐acceptor copolymers poly(dithienosilolo‐carbazole‐alt‐benzothiadiazole) ( PDTSCBT) , poly(dithienocyclopenta‐carbazole‐alt‐benzothiadiazole) ( PDTCCBT), and poly(dithienopyrrolo‐carbazole‐alt‐benzothiadiazole) ( PDTPCBT) . The silole units in DTSC possess electron‐accepting ability that lowers the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of PDTSCBT , whereas stronger electron‐donating ability of the pyrrole moiety in DTPC increases the HOMO and LUMO energy levels of PDTPCBT . The optical bandgaps (E_g^opt) deduced from the absorption edges of thin film spectra are in the following order: PDTSCBT (1.83 eV) > PDTCCBT (1.64 eV) > PDTPCBT (1.50 eV). This result indicated that the donor strength of the heptacyclic arenes is in the order: DTPC > DTCC > DTSC . The devices based on PDTSCBT and PDTCCBT exhibited high hole mobilities of 0.073 and 0.110 cm² V^?1 s^?1, respectively, which are among the highest performance from the OFET devices based on the amorphous donor‐acceptor copolymers. The bulk heterojunction photovoltaic device using PDTSCBT as the p‐type material delivered a promising efficiency of 5.2% with an enhanced open circuit voltage, V_oc, of 0.82 V.     

Red,Green, and Blue Light‐Emitting Polyfluorenes Containing a Dibenzothiophene‐S,S‐Dioxide Unit and Efficient High‐Color‐Rendering‐Index White‐Light‐Emitting Diodes Made Therefrom

A series of blue (B), green (G) and red (R) light‐emitting, 9,9‐bis(4‐(2‐ethyl‐hexyloxy)phenyl)fluorene (PPF) based polymers containing a dibenzothiophene‐S,S‐dioxide (SO) unit (PPF‐SO polymer), with an additional benzothiadiazole (BT) unit (PPF‐SO‐BT polymer) or a 4,7‐di(4‐hexylthien‐2‐yl)‐benzothiadiazole (DHTBT) unit (PPF‐SO‐DHTBT polymer) are synthesized. These polymers exhibit high fluorescence yields and good thermal stability. Light‐emitting diodes (LEDs) using PPF‐SO25, PPF‐SO15‐BT1, and PPF‐SO15‐DHTBT1 as emission polymers have maximum efficiencies LE_max = 7.0, 17.6 and 6.1 cd A^?1 with CIE coordinates (0.15, 0.17), (0.37, 0.56) and (0.62, 0.36), respectively. 1D distributed feedback lasers using PPF‐SO30 as the gain medium are demonstrated, with a wavelength tuning range 467 to 487 nm and low pump energy thresholds (≥18 nJ). Blending different ratios of B (PPF‐SO), G (PPF‐SO‐BT) and R (PPF‐SO‐DHTBT) polymers allows highly efficient white polymer light‐emitting diodes (WPLEDs) to be realized. The optimized devices have an attractive color temperature close to 4700 K and an excellent color rendering index (CRI) ≥90. They are relatively stable, with the emission color remaining almost unchanged when the current densities increase from 20 to 260 mA cm^?2. The use of these polymers enables WPLEDs with a superior trade‐off between device efficiency, CRI, and color stability.     

A Novel Neutral State Green Polymeric Electrochromic with Superior n‐ and p‐Doping Processes: Closer to Red‐Blue‐Green (RGB) Display Realization

Two donor‐acceptor systems, 4,7‐di‐2‐thienyl‐2,1,3‐benzoselenadiazole (TSeT) and 4,7‐di‐2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl‐2,1,3‐benzoselenadiazole (ESeE) are synthesized and electropolymerized to give polymers PTSeT and PESeE, respectively. One of the polymers, PTSeT, is blue‐green in the neutral state and soluble, exhibiting a deep‐red emission color. The other, PESeE, is the first 2,1,3‐benzoselenadiazole‐based neutral state green polymer with a narrow bandgap (1.04 eV). Furthermore, PESeE has superior and durable n‐ and p‐doping processes. Beyond the stability and the robustness, both of the polymer films exhibit multi‐electrochromic behavior.