Naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole‐Containing π‐Conjugated Compound: Nonfullerene Electron Acceptor for Organic Photovoltaics

The development of nonfullerene acceptor materials applicable to organic photovoltaics (OPVs) has attracted considerable attention for the achievement of a high power conversion efficiency (PCE) in recent years. However, it is still challenging due to the insufficiency of both the variety of effective electron‐deficient units and certain guidelines for the design of such materials. This work focusses on naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole (NTz) as a key electron‐deficient unit. Therefore, a new electron‐accepting π‐conjugated compound (NTz‐Np), whose structure is based on the combination of NTz and the fluorene‐containing imide‐annelated terminal units (Np), is designed and synthesized. The NTz‐Np compound exhibits a narrow optical energy gap (1.73 eV), a proper energy level (?3.60 eV) of the lowest unoccupied molecular orbital, and moderate electron mobility (1.6 × 10^?5 cm² V^?1 s^?1), indicating that NTz‐Np has appropriate characteristics as an acceptor against poly(3‐hexylthiophene) (P3HT), a representative donor. OPV devices based on NTz‐Np under the blend with P3HT show high photovoltaic performance with a PCE of 2.81%, which is the highest class among the P3HT/nonfullerene‐based OPVs with the conventional device structure. This result indicates that NTz unit can be categorized as a potential electron‐deficient unit for the nonfullerene acceptors.     

A facile strategy to enhance absorption coefficient and photovoltaic performance of two-dimensional benzo[1,2-b:4,5-b′]dithiophene and thieno[3,4-c]pyrrole-4,6-dione polymers via subtle chemical structure variations

Two novel donor–acceptor (D–A) type conjugated polymers using thiophene and hexyl-thiophene spacers between two-dimensional alkyl-thiophene substituted benzo[1,2-b:4,5-b′]dithiophene (BDT-RT) and alkylthieno[3,4-c]pyrrole-4,6-dione (TPD) units are synthesized and characterized. The effects of incorporation of alkyl-thiophene spacers in the polymer backbone on the optical, electrochemical, charge transport and photovoltaic properties are studied. The bulk-heterojunction (BHJ) polymer solar cells (PSCs) based on the polymer with hexyl-thiophene spacers show much better performance (with power conversion efficiency up to 6.08%) than that of polymer without spacers, which is very distinct from alkyl-thiophene spacer effect of other BDT-TPD structured polymers reported previously. The experimental results and theoretical calculations show that a subtle tuning of chemical structure can significantly influence the absorption coefficient by inserting alkyl-thiophene spacers in the polymer backbone. This provides an important route for designing new materials to obtain higher current density (J_sc) and fill factors (FF).     

Synthesis and Crystal Structure of 1,6:3,4-Bis(1,2-xylyiene) tetrahydro-imidazo[4,5-d]imidazole-2,5(1H,3H)-dione

The compound 1,6∶3,4-Bis(1,2-xylyiene)tetrahydro-imidazo[4,5-d]imidazole-2,5(1H,3H)-dione(C20H18N4O2, Mr=346.38) has been synthesized for the first time. Complete assignments were achieved by 1H NMR, IR, EI-MS, elemental analysis and single-crystal X-ray diffraction technique. The crystal belongs to monoclinic, space group P2(1)/n with a=10.266 0(16), b=11.298 5(18), c=1.452 20(20) nm, β=97.923(3), V=1.668 4(5) nm3, Z=4, Dc=1.379 g/cm3, μ(MoKα)=0.092 mm-1, F(000)=728, R=0.053 2 and wR=0.112 3 for 3632 observed reflections with I>2σ(I). X-ray analysis reveals dimeric aggregates are formed through hydrogen bond and offset π-π stacking. In addition, the compound assembles to a three-dimensional networking structure by other hydrogen bond.     

Recently Advanced Polymer Materials Containing Dithieno[3,2‐b:2′,3′‐d]phosphole Oxide for Efficient Charge Transfer in High‐Performance Solar Cells

Two novel semiconducting polymers based on benzodithiophene and dithienophosphole oxide (DTP) units are designed and synthesized. A novel electron‐deficient DTP moiety is developed. Surprisingly, the introduction of DTP units brings highly polarizable characteristics, which is beneficial for the photocurrent in solar cells. Thus, the donor–acceptor type of conjugated polymers based on this novel acceptor has superior charge transfer properties and highly efficient PL quenching efficiencies. As a result, polymer solar cells (PSCs) with high power conversion efficiencies of 6.10% and 7.08% are obtained from poly(3,5‐didodecyl‐4‐phenylphospholo[3,2‐b:4,5‐b']dithiophene–4‐oxide‐alt‐4,8‐bis(5‐decylthiophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene) (PDTP–BDTT) and PDTP–4‐oxide‐alt‐4,8‐bis(5‐decylselenophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene) (PDTP–BDTSe), respectively, when the photoactive layer is processed with the 1,8‐octanedithiol (ODT) additive. The PDTP–BDTSe copolymer is now the best performing DTP‐based material for PSCs. Using the polarizable unit strategy determined in this study for the molecular design of conjugated polymers is expected to greatly advance the development of organic electronic devices.     

Dithieno[3,2‐b:2′,3′‐d]pyrrol‐Cored Hole Transport Material Enabling Over 21% Efficiency Dopant‐Free Perovskite Solar Cells

Dopant‐free hole transport materials (HTMs) are essential for commercialization of perovskite solar cells (PSCs). However, power conversion efficiencies (PCEs) of the state‐of‐the‐art PSCs with small molecule dopant‐free HTMs are below 20%. Herein, a simple dithieno[3,2‐b:2′,3′‐d]pyrrol‐cored small molecule, DTP‐C6Th, is reported as a promising dopant‐free HTM. Compared with commonly used spiro‐OMeTAD, DTP‐C6Th exhibits a similar energy level, a better hole mobility of 4.18 × 10^?4 cm² V^?1 s^?1, and more efficient hole extraction, enabling efficient and stable PSCs with a dopant‐free HTM. With the addition of an ultrathin poly(methyl methacrylate) passivation layer and properly tuning the composition of the perovskite absorber layer, a champion PCE of 21.04% is achieved, which is the highest value for small molecule dopant‐free HTM based PSCs to date. Additionally, PSCs using the DTP‐C6Th HTM exhibit significantly improved long‐term stability compared with the conventional cells with the metal additive doped spiro‐OMeTAD HTM. Therefore, this work provides a new candidate and effective device engineering strategy for achieving high PCEs with dopant‐free HTMs.     

Synthesis,Characterization, and Field‐Effect Transistor Performance of Thieno[3,2‐b]thieno[2′,3′:4,5]thieno[2,3‐d]thiophene Derivatives

The synthesis, characterization, and field‐effect transistor (FET) properties of a new class of thieno[3,2‐b]thieno[2′,3′:4,5]thieno[2,3‐d]thiophene derivatives are described. The optical spectra of their films show the presence of stronger interactions between molecules in the solid state. Thermal analyses reveal that the three materials are thermally stable and have no phase transitions at low temperature. The crystal structures are determined, and show π‐stacked structures and intermolecular S···S contacts. These organic materials exhibit p‐type FET behavior with hole mobilities as high as 0.14 cm² V^?1 s^?1 and an on/off current ratio of 10⁶. These results indicate that thieno[3,2‐b]thieno [2′,3′:4,5]thieno[2,3‐d]thiophene, as a linear π‐conjugated system, is an effective building block for developing high‐performance organic semiconductors.     

A wide-bandgap copolymer donor with a 5-methyl-4H-dithieno[3,2-e:2',3'-g]isoindole-4,6(5H)-dione unit

Wide-bandgap copolymer donors with fused-ring accept-or units (FAUs) present excellent performance in non-fullerene organic solar cells due to their complementary light-absorption with nonfullerene acceptors,deep the highest occupied molecular orbital (HOMO) levels and high hole mobilities[1-4].A bunch of FAU-based copolymer donors were developed in recent years,such as PM6[s],PM7[6],PBQx-TCI[7],PTQ10[8],PBQ6[9],P2F-EHp[10],D16[11],L1-S[12],D18[13,14]and D18-CI[1s,16].They delivered ＞16％ power conversion effi-ciencies (PCEs) in solar cells.To develop good FAUs is the key toward efficient FAU-based copolymer donors.A good FAU generally has a strong electron-withdrawing character that leads to a low HOMO level and a high open-circuit voltage(Voc),and a relatively large molecular plane that facilitates poly-mer stacking and enhances hole mobility.Recently,we de-veloped copolymer donors D18 and D18-CI by using dithi-eno[3',2':3,4;2",3":5,6]benzo[1,2-c][1,2,5]thiadiazole (DTBT)unit[13] (Fig.1(a)).Thanks to the strong electron-withdrawing property and the rigid and extended molecular plane of DTBT,D18 and D18-CI deliver outstanding PCEs up to 18.69％[13-16].The success of D18 polymers stimulated us to design more high-performance copolymer donors with nov-el FAUs.In this work,we designed a wide-bandgap copoly-mer donor P1 by using a fused-ring imide building block,5-methyl-4H-dithieno[3,2-e:2',3'-g]isoindole-4,6(5 H)-dione(MDTID).Compared with the thiadiazole moiety in DTBT,the imide moiety in MDTID is more electron-withdrawing.The density functional theory (DFT) calculations show that MDTID has deeper HOMO and the lowest unoccupied molecular orbit-al (LUMO) levels than DTBT,suggesting the stronger electron-accepting capability of MDTID (Fig.1(a)).DFT calculations also indicate that MDTID leads to a deeper HOMO for P1 than that of D18,thus benefiting Voc (Fig.S1).     

Reactions of GaX3 (x  br,i) with AS(SiMe3)3; crystal structures of I3Ga · as(SiMe3)3 and [I2GaAS(sime3)2]2

Reactions of GaX₃ (X ? Br, I) with As(SiMe₃)₃ in 1:1 and 2:1 mole ratios were investigated. For the latter reactant stoichiometry, substances having the empirical formulae AsBr₃Ga₂ (1) and Asl₃Ga₂ (2), the analogues of the previously reported single-source GaAs precursor (AsCl₃Ga₂)_n, were isolated as yellow isolated as yellow insoluble powders. Low-temperature reactions in a 1:1 mole ratio resulted in the isolation of the adducts Br₃Ga.As(SiMe₃)₃ (3) and I₃Ga.As(SiMe₃)₃ (4). On the other hand, at room temperature the GaBr₃ reaction resulted in a complex mixture from which no characterizable compounds were isolated, whereas the Gal₃ reaction afforded the crystalline compound [I₂GaAs(SiMe₃)₂]₂ (5). The structures of 4 and 5 were elucidated by complete single-crystal X-ray analysis (crystal data: 4, monoclinic, space group P2₁/c, a = 16.497(2) Å, b = 9.629(1) Å, c = 16.658(2) Å, β = 113.21(1)°, V = 2432(1) ų, Z = 4; 5, orthorhombic, space group Pbca, a = 14.279(2) Å, b = 17.509(2) Å, c = 13.818(2), Å, V = 3455(1) ų, Z = 4).     

[Fe3(HCOO)6]: A Permanent Porous Diamond Framework Displaying H2/N2 Adsorption,Guest Inclusion,and Guest‐Dependent Magnetism

The porous magnet [Fe₃(HCOO)₆], the iron member of the [M₃(HCOO)₆] family (where M = Mn, Fe, Co, Ni, etc.), based on a diamond framework consisting of Fe‐centered FeFe₄ tetrahedral nodes, is prepared successfully by using a solution‐chemistry method. The as‐prepared compound, [Fe₃(HCOO)₆](CH₃OH)_1.5(H₂O)_0.5 ( 1 ‐ parent ), exhibits facile removal of its guests, methanol, and water, to give the desolvated framework [Fe₃(HCOO)₆] ( 2 ‐ empty ) that displays permanent porosity and thermal stability up to 270 °C. The flexibility of the framework and the amphiphilic nature of the surface of the pores consisting of both C–H and O arrays allows 2 ‐ empty to take up significant H₂ and N₂ at liquid‐nitrogen temperatures and a wide spectrum of both polar and nonpolar guests of different sizes. A series of guest‐inclusion compounds, [Fe₃(HCOO)₆](I₂)_0.84 ( 3 ‐ iodine ), [Fe₃(HCOO)₆](C₄H₈O) ( 4 ‐ THF ), [Fe₃(HCOO)₆](C₄H₄O) ( 5 ‐ furan ), [Fe₃(HCOO)₆](C₆H₆) ( 6 ‐ benzene ), [Fe₃(HCOO)₆](CH₃CN) ( 7 ‐ acetonitrile ), and [Fe₃(HCOO)₆]((CH₃)₂CO) ( 8 ‐ acetone ) are successfully prepared by vapor diffusion of the guest into the pores of 2 ‐ empty and their structures are characterized by using single‐crystal X‐ray crystallography. Zigzag molecular arrays of the guest are formed in the confined channels of the host framework, and the weak hydrogen‐bonding provides the main host–guest interaction. All the compounds show 3D long‐range magnetic ordering and guest‐modulated Curie temperatures, coercive fields, and remnant magnetization as a consequence of the subtle rearrangement of the magnetic framework that conforms to the size of the guests and the difference in host–guest interactions. A possible magnetic structure of the framework is proposed to account for magnetic competition and geometrical frustration. The thermal and spectroscopic properties of the compounds are also reported.     

Molecular Metals Based on BEDT‐TTF Radical Cation Salts with Magnetic Metal Oxalates as Counterions: β″‐(BEDT‐TTF)4A[M(C2O4)3]·DMF (A = NH4+, K+; M = CrIII,FeIII)

Four (BEDT‐TTF)₄A[M(C₂O₄)₃]·DMF (DMF = dimethylformamide) salts of the organic donor molecule bis(ethylenedithio)tetrathiafulvalene (BEDT‐TTF) with metal oxalate anions, where A = (NH₄, K), M = Cr ( 1 ); A = NH₄, M = Fe ( 2 ); A = K, M = Cr ( 3 ); and A = NH₄, M = Cr ( 3′ ) were prepared by electrocrystallization. These salts were characterized by single‐crystal X‐ray diffraction, electron spin resonance (ESR) spectroscopy, electrical resistance measurements, and electronic band structure calculations. The structures (with space group C2/c) consist of alternating β″‐type layers of BEDT‐TTF and an approximately hexagonal network formed by the A⁺ cation and the metal, with the solvent molecule, DMF, occupying hexagonal cavities in the anion layer. All of the salts are two‐dimensional organic metals down to 4.2 K and do not exhibit superconductivity. Their electronic band structure is similar to that of the known organic superconductor β″‐(BEDT‐TTF)₄H₃O[Fe(C₂O₄)₃]·BN. The ESR spectra of salts 1 and 3′ are characterized by two resonances, one of Gaussian shape arising from the 3d localized electrons of Cr³⁺ and the other of Lorentzian (and Dysonian) shape due to the conduction electrons in the organic layers. On the basis of the calculated Fermi surfaces it is suggested that these salts could exhibit an interesting magnetoresistance behavior if disorder does not prevent the observation of the Shubnikov‐de Haas oscillations.