Ping Shen

Synthesis and photovoltaic properties of polythiophene stars with porphyrin core

Two novel porphyrin-polythiophene star-shaped polymer (P-bs1 and P-bs2) containing triphenylamine terminated poly(3′-hexyl-2,2′-bithiophene) and poly(3′-hexyl-2,2′-bithiophene) as four arms in the peripheral of porphyrin core were synthesized by Stille reaction. The thermal, photophysical, electrochemical and photovoltaic properties of the porphyrin-polythiophene derivatives were investigated. The porphyrin-polythiophene derivatives showed broad absorption in the region of 350 ∼ 650 nm. In particular, the absorption intensity at 450 ∼ 650 nm was greatly enhanced for the meso-substituted polythiophene derivatives, P-bs2. The photoluminescence spectra indicated that the emission peaks of porphyrin units were suppressed by the intensive emission of thiophene units. The electrochemical properties indicated that the porphyrin-polythiophene derivatives are potential electron-donor materials for bulk heterojunction solar cells and dye-sensitized solar cells (DSSCs). Polymer bulk heterojunction solar cells based on P-bs2:PCBM (1:1, w/w) showed power conversion efficiencies (PCE) up to 0.61% under the illumination of AM 1.5, 100 mW cm−2, which increased by 69% compared to that of P-bs1 (0.36%). Meanwhile, higher PCE of 2.17% and 3.91% based on P-bs1 and P-bs2 polymer-sensitized solar cells were attained. The better photovoltaic properties benefited from longer arms of polythiophene derivatives.

Synthesis and photovoltaic performances of conjugated copolymers with 4,7-dithien-5-yl-2,1,3-benzothiadiazole and di(p-tolyl)phenylamine side groups

Three new copolymers (PT-TPA, PT-DTBT and PT-DTBTTPA) based on benzo[1,2-b:4,5-b]dithiophene (BDT) and thiophene with different conjugated side chains (di(p-tolyl)phenylamine (TPA), 4,7-dithien-5-yl-2,1,3-benzothiadiazole (DTBT) and DTBT-TPA) were synthesized via Stille coupling polymerization. The TPA and the DTBT were introduced to improve the hole-transport ability and broaden the absorption spectrum. The effects of different conjugated side groups on thermal, optical, electrochemical, hole-transporting and photovoltaic properties of these copolymers were investigated. Field effect results show that the copolymer PT-DTBTTPA containing TPA and DTBT in the side chain showed the highest hole mobility. The three copolymers exhibit deep-lying HOMO energy levels, which were effectively tuned by changing the side groups. Photovoltaic cells were fabricated with the synthesized copolymers as electron donors and [6,6]-phenyl-C-butyric acid methyl ester (PCBM) as the electron acceptor. Bulk heterojunction polymer solar cells based on PT-DTBT and PT-DTBTTPA showed promising power conversion efficiencies of 5.50% and 5.16%, respectively.

Side-chain engineering of benzodithiophene–thiophene copolymers with conjugated side chains containing the electron-withdrawing ethylrhodanine group

Four benzodithiophene (BDT)-thiophene (T) copolymers with conjugated side chains containing electron-withdrawing ethylrhodanine acceptor units, PHDBDT-T-R, PEHBDT-T-R, PHDBDT-T-TR, and PEHBDT-T-TR, were designed and synthesized for investigating the effect of side chains on the physicochemical properties and photovoltaic performance of the conjugated polymers. All the four copolymers possess an identical conjugated backbone of alternative benzodithiophene-thiophene, but different side chains on BDT and thiophene units, respectively. Polymer solar cells (PSCs) with these polymers as donors and PC70BM as acceptors exhibit an initial power conversion efficiency (PCE) of 0.61% for PHDBDT-T-R, 2.32% for PEHBDT-T-R, 1.46% for PHDBDT-T-TR, and 2.36% for PEHBDT-T-TR. After the treatment with 3 vol% DIO additive and with methanol, the highest PCE was increased up to 1.01%, 4.04%, 3.47%, and 4.25% for PHDBDT-T-R, PEHBDT-T-R, PHDBDT-T-TR, and PEHBDT-T-TR, respectively, with significantly increased J(sc) and FF. The effects of methanol treatment on the photovoltaic performance of the PSCs can be ascribed to the increased carrier transport, improved exciton dissociation and optimized phase separation of the active layer. This work indicates that side-chain engineering plays a key role in molecular structures and optoelectronic properties.

Synergetic Effect of Efficient Energy Transfer and 3D π−π Stack for White Emission Based on the Block Copolymers Containing Nonconjugated Spacer

A series of block copolymers containing nonconjugated spacer and 3D pi-pi stacking structure with simultaneous blue-, green-, and yellow-emitting units has been synthesized and characterized. The dependence of the energy transfer and electroluminescence (EL) properties of these block copolymers on the contents of oligo(phenylenevinylene)s has been investigated. The block copolymer (GEO8-BEO-YEO4) with 98.8% blue-emitting oligomer (BEO), 0.8% green-emitting oligomer (GEO), and 0.4% yellow-emitting oligomer (YEO) showed the best electroluminescent performance, exhibiting a maximum luminance of 2309 cd/m(2) and efficiency of 0.34 cd/A. The single-layer-polymer light-emitting diodes device based on GEO2-BEO-YEO4 emitted greenish white light with the CIE coordinates of (0.26, 0.37) at 10 V. The synergetic effect of the efficient energy transfer and 3D pi-pi stack of these block copolymers on the photoluminescent and electroluminescent properties are investigated.

EFFICIENT TiO2 NANOPARTICLES/NANORODS COMPOSITE ELECTRODES FOR DYE-SENSITIZED SOLAR CELLS

A new TiO2 nanoparticles/nanorods composite electrode was fabricated and applied in dye-sensitized solar cells (DSSCs). The TiO2 nanorods were obtained by grinding the electrospun TiO2 nanofibers mechanically. The composite photoanode of dye-sensitized solar cells was fabricated by using TiO2 nanoparticles (P25) and electrospun TiO2 nanorods. At the optimized condition, the power conversion efficiency (η) based on a triphenylamine dye (SD2) and a ruthenium dye (N719) are 8.28% and 8.80% under AM 1.5 illumination (100 mW ⋅ cm-2), respectively. The results show that the electrospun TiO2 nanorods in the composite photoanode improve the physicochemical properties and enhance the photovoltaic performances of solar cells.

Achieving efficient thick active layer and large area ternary polymer solar cells by incorporating a new fused heptacyclic non-fullerene acceptor

Nowadays, constructing ternary polymer solar cells (PSCs) and developing non-fullerene acceptors (NFAs) have emerged as two powerful and efficient means to propel the device efficiency further forward. However, the incorporation of NFAs into a fullerene-based binary PSC to form high-performance donor : fullerene : NFA type ternary PSCs with a thick active layer and large area is still a challenge due to their inferior charge transport properties, complicated blend morphology and unclear aggregation behavior. In this contribution, a new low bandgap NFA (DTCFOIC) based on a fused heptacyclic core (dithienocyclopentafluorene) is developed and blended with a medium bandgap polymer donor PBDB-T to form a binary PSC achieving a power conversion efficiency (PCE) of 6.92%. When a small amount of DTCFOIC was employed as the additional acceptor combined with fullerene-based PC71BM to construct the PBDB-T : PC71BM : DTCFOIC ternary PSCs, an enhanced PCE of 9.40% was obtained after carefully optimizing the blend composition and the amount of the additive 1,8-diiodooctane (DIO) with a thin active layer (100 nm) and normal area (0.04 cm2). This could be mainly attributed to the extended absorption range, improved charge transfer, dissociation and collection properties, and suppressed charge recombination as well as optimized blend morphology in the ternary blend after the addition of NFA and DIO. Moreover, the photovoltaic performance of the ternary PSCs could be further optimized to achieve a higher PCE of 10.13% with a thicker active layer (160 nm) and eventually the highest PCE of 10.41% can be achieved with a thick active layer of 190 nm and a large area of 0.1 cm2, which is among the highest efficiencies of both thick layer and large area ternary PSCs. Besides, the ternary PSCs preserved a high PCE over 9% even with a larger active area of 1 cm2 using a thick active layer (172 nm). This observation demonstrates that incorporating a NFA to construct donor : fullerene : NFA type ternary PSCs is a feasible and effective approach to significantly enhance the performance of the resulting ternary system. Meanwhile, our results related to the thick active layer and large area suggest that this ternary system has a promising application prospect for mass manufacturing high-performance PSCs with a roll-to-roll process.

Erratum: Development of a new benzo(1,2-b:4,5-b′)dithiophene-based copolymer with conjugated dithienylbenzothiadiazolevinylene side chains for efficient solar cells (Chemical Communications (2011) (9381-9383) (DOI: 10.1039/c1cc12851e))

Although the work published in this paper proved reproducible by at least three different researchers in the St. Andrews laboratories, it could not be reproduced elsewhere, nor could it be reproduced in St. Andrews when we changed to a different batch of 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos). Subsequent study has now produced a protocol which is reproducible not only in our hands but also in the laboratories of Professor Walter Leitner and Dr. Jürgen Klankermeyer at RWTH, Aachen. Full details of the new procedure will be published elsewhere, but we report below an example for the hydrogenation of acetanilide as carried out in St. Andrews and Aachen.