Jing Ge

Thermopower enhancement in conducting polymer nanocomposites via carrier energy scattering at the organic–inorganic semiconductor interface

The energy-filtering effect was successfully employed at the organic–inorganic semiconductor interface of poly(3-hexylthiophene) (P3HT) nanocomposites with the addition of Bi2Te3 nanowires, where low-energy carriers were strongly scattered by the appropriately engineered potential barrier of the P3HT–Bi2Te3 interface. The resulting P3HT–Bi2Te3 nanocomposites exhibited a high power factor of 13.6 μW K−2 m−1 compared to that of 3.9 μW K−2 m−1 in P3HT. The transport characteristics of nanocomposites, including the carrier concentration, mobility, and energy-dependent scattering parameter, were revealed by the experimental measurements of electrical conductivity, Seebeck coefficient, and Hall coefficient to quantitatively elucidate the carrier energy scattering at the P3HT–Bi2Te3 interface. The ability to rationally engineer the organic–inorganic semiconductor interfaces of polymer nanocomposites to achieve an improved Seebeck coefficient and power factor provides a potential route to high-performance, large-area, and flexible polymer thermoelectric materials.

All-conjugated poly(3-alkylthiophene) diblock copolymer-based bulk heterojunction solar cells with controlled molecular organization and nanoscale morphology

Control over the ratio of two blocks in a new class of all-conjugated diblock copolymers, poly(3-butylthiophene)-b-poly(3-hexylthiophene) (P3BHT), provides a facile approach to precisely tune the molecular organization and nanoscale morphology in polymer bulk heterojunction (BHJ) solar cells. In stark contrast to the power conversion efficiency, PCE, of 1.08% in poly(3-butylthiophene) (P3BT)/[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) and 3.54% in poly(3-hexylthiophene) (P3HT)/PC71BM solar cells, an attractive, high PCE of 4.02% was achieved in a P3BHT21/PC71BM BHJ device in which the molar ratio of P3BT : P3HT in P3BHT21 was 2 : 1. The ratio of P3BT and P3HT blocks was found to exert a noteworthy influence on the molecular organization of P3BHT, the film morphology of P3BHT/PC71BM blend, and the final performance of P3BHT/PC71BM photovoltaic devices. This enhanced performance reflected a synergy of finer phase separation of P3BHT21 and PC71BM and the formation of respective percolation networks of electron donor P3BHT and electron acceptor PC71BM. The P3HT block rendered the P3BHT chains with favorable chemical compatibility for the diffusion of PC71BM molecules, allowing for finer phase separation between P3BHT crystalline domains and PC71BM domains at the nanoscale and maximizing the interfacial area of P3BHT21/PC71BM for improved charge generation. The P3BT block facilitated the self-assembly of P3BHT chains into sufficient interpenetrating pathways for efficient charge transport and collection. Moreover, a small crystalline domain with a size of 10.4 nm formed in the active layer that is comparable to the exciton diffusion length of most conjugated polymers (∼10 nm).

Microphase separation-promoted crystallization in all-conjugated poly(3-alkylthiophene) diblock copolymers with high crystallinity and carrier mobility

The crystallinity of all-conjugated diblock copolymer, poly(3-butylthiophene)-b-poly(3-dodecylthiophene) (P3BDDT), with varied block ratios was significantly enhanced by a “two-step” thermal annealing treatment. The resulting P3BDDT exhibited an attractively high crystallinity of ∼35%, which is a 3-fold enhancement over those of its homopolymer counterparts. The space-charge limited current (SCLC) mobility measurement revealed that the carrier mobility of the highly crystalline P3BDDT film was increased to as high as ∼8.4 × 10−3 cm2 V−1 s−1, exceeding the highest SCLC mobility of poly(3-alkylthiophene) homopolymer films reported in previous work (i.e., ∼1.6 × 10−3 cm2 V−1 s−1). DSC, XRD, AFM and SAXS characterizations demonstrated that the interplay of crystallization and microphase separation during the “two-step” thermal annealing treatment plays a key role in the improvement of P3BDDT crystallinity.

Transition from polythiophene-based one-dimensional nanofibers to spherical clusters in ultrafiltration

We report the behavior of one-dimensional polythiophene-based nanofibers in solutions passing through the nanopores under a flow field. Under a strong flow field, a fiber-to-cluster transition can be observed when the nanofiber solution concentration is above a critical value. The Zimm time and the passing time of the nanofibers are compared to explain the way the nanofibers pass through the nanopores under different flow fields.