当前位置:文库下载 > 所有分类 > 工程科技 > 能源/化工 > 高效小分子材料
免费下载此文档侵权投诉

高效小分子材料

高效小分子材料

www.advenergymat.de

http://www.wenkuxiazai.com

nsymmetrical Triphenylamine-Oligothiophene Hybrid U

Conjugated Systems as Donor Materials for High-Voltage Solution-Processed Organic Solar Cells

Emilie Ripaud, Théodulf Rousseau, Philippe Leriche,* and Jean Roncali*

uring the past decade, interest in organic solar cells has D

increased at a considerable pace due to the promise of pro-ducing low-cost solar electricity with light-weight devices and low environmental impact technologies. Among the different architectures of organic solar cells, solution-processed bulk hetero junctions (BHJ) present the advantage of being compatible with large-area exible substrates and low-energy-consumption

[1–6]fabrication processes. The tremendous research effort

invested in the chemistry of active materials and device tech-nology during the past few years has generated impressive progress, and power conversion ef ciencies in the 6.0–8.0% range have been reported for BHJ cells based on low bandgap

[4–6]conjugated polymers and acceptors based on C 70fullerene.

In spite of these results, the problems inherent to the synthesis, reproducibility, and puri cation of polydisperse π-conjugated polymers has triggered the emergence of an alternative approach based on the use of small soluble molecules as donor

[7–12materials for solution-processed BHJ solar cells. ]

Starting from modest initial power conversion ef ciencies

[7,12]of 0.20–0.30%, the performances of molecular BHJ solar

cells have rapidly progressed thanks in particular to the devel-[7–26opment of a large variety of new molecular donors. ] Thus, a

power conversion ef ciency (PCE) of 4.40% has been published for a cell based on a diketopyrrolopyrrole donor and PC 71BM

[25]acceptor, while quite recently a PCE of 4.30% was reported

for a cell based on PC BM and a triphenylamine derivative 71

containing benzothiadiazole electron de cient units as donor

[26]material.

During the past few years, molecular donors based on

triphenylamine (TPA) derivatives have attracted special

[13interest, , 27–41 ] in particular because TPA represents an inter-esting platform for the development of processable organic

[27]glasses with isotropic electronic properties.

We have shown already that the grafting of terthienyl

branches on a TPA core leads to a p-type organic semicon-ductor ( 1 ) with high hole mobility ( Scheme 1). Thus, μ FET

2 1 1 values of 0.01 cm V s were determined for eld-effect tran-sistors based on vacuum deposited thin lms of 1.[28 ] On the

other hand, the introduction of electron-withdrawing groups

on hybrid TPA-based conjugated systems produces an internal charge-transfer (ICT) which lowers the highest occupied mole-cular orbital (HOMO) level and reduces the optical bandgap of the corresponding material. These combined effects produce a red-shifted extension of the photoresponse of the resulting solar cells and a large increase of the open-circuit voltage ( V oc)[13]and conversion ef ciency.

Systematic analyses of structure-properties relationships in

TPA-based systems with various acceptor groups have shown that the HOMO and lowest unoccupied molecular orbital (LUMO) levels, the absorption maximum and the relative inten-sity of the ICT band depend on the number and nature of the

[13electron-acceptor groups. , 29 ] Thus, compound 2 with three

(dicyanovinyl)-thienyl branches led to vacuum deposited bilayer

[30solar cells with 1.85% PCE and a Voc as high as 1.15 V. ] How-ever, the solution processability of this donor was insuf cient to

allow the fabrication of solution-processed BHJ solar cells.

In an attempt to solve this problem, we report here the

synthesis of unsymmetrical conjugated TPA donors ( 3,4)in which the introduction of one or two oligothiophene branches end-capped with hexyl chains is expected to improve solubility, and thus to allowing the fabrication of solution-processed BHJ. Furthermore, as recently observed for BODIPY (borondipyr-romethene) donors, the introduction of short-chain oligothi-ophenes in the structure can be expected to improve the hole-mobility and thus the conversion ef ciency of the resulting

[22]solar cells. Finally, it is worth noting that the development

of unsymmetrical TPA derivatives can contribute to enlarge the potentialities of this class of donor materials. The synthesis and characterization of the electronic properties of these new TPA-based conjugated systems is presented together with a rst evaluation of their performances as donor material in mole-cular BHJ solar cells.

The synthesis of compounds 3 and 4 is depicted in Scheme 2. Carboxaldehydes 9 and 10 were prepared by formyla-tion of tris(2-thienyl)triphenylamine according to a previ-[13ously reported procedure. ] Bromination of 9 and 10with N -bromosuccinimide gave bromo compounds 7 and 8 in 88 and 93% yield respectively. A Stille coupling reaction between 7 and 8 and 5-trimethylstannyl-5’-hexyl-2,2’-bithiophene led to aldehydes 5 and 6 which were nally condensed with malonod-initrile in the presence of triethylamine to give the target com-pounds 3 and 4 in 28 and 38% isolated yield for the two steps. Figure 1 shows the UV-vis absorption spectra of compounds 3 and 4 in CH . Both spectra show a rst transition around 2Cl 2 400 nm attributed to a π– π * transition and a second band in the 500 nm region assigned to an intramolecular charge transfer between the thienyl-substituted TPA block and the terminal

Dr. E. Ripaud ,T. Rousseau ,Prof. P. Leriche ,Dr. J. Roncali Group Linear Conjugated SystemsCNRS Moltech-AnjouUniversity of Angers

2Bd Lavoisier, 49045 Angers, France

E-mail: [email protected]; [email protected]://www.hjavira.net DOI: 10.1002/aenm.201100065 540

高效小分子材料

高效小分子材料

高效小分子材料

http://www.hjavira.net© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimAdv. Energy Mater. 2011, 1, 540–545

第1页

免费下载Word文档免费下载:高效小分子材料

(下载1-6页,共6页)

我要评论

返回顶部