Selenium Substitution in Bithiophene Imide Polymer Semiconductors Enables High-Performance n-Type Organic Thermoelectric

Designing n-type polymers with high electrical conductivity remains a major challenge for organic thermoelectrics (OTEs). Herein, by devising a novel selenophene-based electron-deficient building block, the pronounced advantages of selenium substitution in simultaneously enabling advanced n-type polymers is demonstrated with high mobility (≈2 orders of magnitude higher versus their sulfur-based analogues due to both intensified intra- and inter-chain interactions) and much improved n-doping efficiency (enabled by the largely lowered LUMO level with a ≈0.2 eV margin) of the resulting polymers. Via side chain optimization and donor engineering, the selenium-substituted polymer, f-BSeI2TEG-FT, achieves a highest conductivity of 103.5 S cm⁻¹ and power factor of 70.1 µW m⁻¹ K⁻², which are among the highest values reported in literature for n-type polymers, and f-BSeI2TEG-FT greatly outperformed the sulfur-based analogue polymer by 40% conductivity increase. These results demonstrate that selenium substitution is a very effective strategy for improving n-type performance and provide important structure-property correlations for developing high-performing n-type OTE materials.     

路易斯碱负离子掺杂有机半导体:原理、应用和展望

掺杂是改善有机半导体载流子浓度和电荷输运能力的有效方法.路易斯碱负离子电子转移掺杂有机半导体,逐渐发展成为了一种温和、可控和可溶液加工的n型掺杂方法,并在有机光电器件中展现出较好的应用.本综述旨在探讨路易斯碱负离子和n型半导体之间的电子转移机制及其影响因素,总结基于该策略开发的界面材料和活性层掺杂等方面的应用,并展望其未来的发展方向.     

EQCM study of the p- and n-doping processes of a poly[4,4-bis(butylsulphanyl)-2,2-bithiophene]

Electrogenerated deposits of poly[4,4^′-bis(butylsulphanyl)-2,2^′-bithiophene] have been characterised in the presence of different supporting electrolytes, by coupling current (charge) to microgravimetric measurements from the electrochemical quartz crystal microbalance (EQCM). The simultaneous collection of voltammetric measurements and of data relative to mass changes shows the influence exerted by the nature of the supporting electrolyte on the charge-discharge steps of both p- and n-doping processes. Interestingly, the microgravimetric data collected corresponding to the pre-peaks of both doping processes suggest the occurrence of two opposite motions of ions (ingress into and exit out from the polymer) in the relevant potential region, giving a contribution to the study of the `residual charge' phenomenon.     

A comparison of two air-stable molecular n-dopants for C60

We compare two air-stable n-dopants for the fullerene C₆₀: AOB and DMBI-POH. Conductivity and Seebeck coefficient measurements were performed at various doping concentrations and the thermal activation of the conductivity was determined. A superlinear increase of conductivity upon doping was found for DMBI-POH doped C₆₀ reaching a maximum conductivity of 5.3 S/cm. In contrast to this, a linear rise of conductivity and an exponential thermal activation of mobility was observed for C₆₀ doped by AOB. This suggests a different doping mechanism for the two compounds.     

具有新型电子传输层的有机薄膜电致发光器件

将8-hydroxy-quinolinato lithium(Liq)掺入4'7-diphyenyl-1,10-phenanthroline(BPhen)作为n型电子传输层(ETL),将tetrafluro-tetracyano-quinodimethane(F4-TCNQ)掺入4,4',4"-tris(3-methylphenylphenylamono)triphenylamine(m-MTDATA)作为p型空穴传输层(HTL),制作了p-i-n结构有机电致发光器件.为了检验传输层传导率的改善情况,制备了一系列单一空穴器件和单一电子器件.在引入BPhen:33wt% Liq作为ETL后,x% F4-TCNQ:m-MTDATA作为HTL后,器件的电流和功率效率明显改善.与控制器件(未掺杂)相比,性能最佳的掺杂器件的电流及功率效率分别提高了51%和89%,电压下降了29%.这是由于传输层传导能力的提高使得载流子在发光区域达到有效平衡.     

具有新型电子传输层的有机薄膜电致发光器件

将8-hydroxy-quinolinato lithium(Liq)掺入4'7-diphyenyl-1,10-phenanthroline(BPhen)作为n型电子传输层(ETL),将tetrafluro-tetracyano-quinodimethane(F4-TCNQ)掺入4,4',4"-tris(3-methylphenylphenylamono)triphenylamine(m-MTDATA)作为p型空穴传输层(HTL),制作了p-i-n结构有机电致发光器件.为了检验传输层传导率的改善情况,制备了一系列单一空穴器件和单一电子器件.在引入BPhen:33wt% Liq作为ETL后,x% F4-TCNQ:m-MTDATA作为HTL后,器件的电流和功率效率明显改善.与控制器件(未掺杂)相比,性能最佳的掺杂器件的电流及功率效率分别提高了51%和89%,电压下降了29%.这是由于传输层传导能力的提高使得载流子在发光区域达到有效平衡.     

Electrochemical materials science: calculation vs. experiment as predictive tools in tailoring intrinsically conducting polythiophenes

A series of 3-(p-X-phenyl)thiophene monomers (X = −H, –CH₃, –OCH₃, –COCH₃, –COOC₂H₅, –NO₂) was electrochemically polymerized to furnish polymer films that could be reversibly reduced and oxidized (n- and p-doped). The oxidation potentials of the monomers and formal potentials of the n- and p-doping processes of polymers were correlated with resonance and inductive effects of the substituents on the phenyl ring as well as the ionization potentials of the monomers calculated via density function theory, which correspond to the energies for generating radical cations during oxidative processes.     

Realizing p-Type and n-Type Doping of a Single Conjugated Polymer via Incorporation of a Thienoisatin-Terminated Quinoidal Unit

Selective doping of a single conjugated polymer (CP) to obtain p-type and n-type conductive materials would be highly attractive for organic thermoelectric applications, because it will greatly reduce the time and costs of synthesizing different types of CPs. However, this strategy has rarely been investigated. In this study, two CPs are synthesized, designated PTQDPP-T and PTQDPP-2FT, based on a newly developed quinoidal unit with thienoisatin as the termini and a thiophene-flanked diketopyrrolopyrrole (ThDPP) unit as the quinoidal core. The electron-rich thiophene rings in thienoisatin and the electron delocalization induced by thienoisatin resulted in polymers with high-lying highest occupied molecular orbital, and the electron-deficient nature of ThDPP unit and its quinoidal backbone endowed the polymers with low-lying lowest unoccupied molecular orbitals. As a result, both polymers can be p-type and n-type doped. Because of its high mobility, doped PTQDPP-2FT performed better in organic thermoelectric devices than the doped PTQDPP-T. After being doped with FeCl₃ and N-DMBI, PTQDPP-2FT showed p-type and n-type power factors of 278.2 and 2.37 µW m⁻¹ K⁻², respectively. These are the best for bipolar (p-type and n-type) performances that obtained by selective doping of a single polymer.