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arXiv 1206.4529cond-mat.mtrl-scicond-mat.soft
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低带隙给体-受体共聚物及其共混物的激发动力学

Excitation Dynamics in Low Band Gap Donor-Acceptor Copolymers and Blends

Björn Gieseking, Berthold Jäck, Eduard Preis, Stefan Jung, Michael Forster, Ullrich Scherf, Carsten Deibel, Vladimir Dyakonov

摘要:

给体-受体(D-A)型共聚物在有机太阳能电池活性层中显示出巨大的应用潜力。然而,光激发后的激发态的性质、耦合机制和弛豫途径还有待阐明。我们进行了比较测量的稳态吸收和光致发光(PL)的共聚物聚[N-(1-辛基壬基)-2,7-咔唑] -alt-5,5-[4 ',7' -二(噻吩-2-基)-2 ',1',3 ' -苯并噻二唑](PCDTBT)、其结构单元以及新合成的N-(1-辛基壬基)-2,7-双-[(5-苯基)噻吩-2-基)咔唑(BPT-咔唑)(见图1)。PCDTBT的高能吸收带(HEB)被确定为具有相邻噻吩环的咔唑的吸收,而低能吸收带(LEB)则起源于具有相邻苯并噻二唑基团的上述单元上离域的电荷转移(CT)状态。HEB的光激发之后是内部弛豫之前的辐射衰减到基态。加入PC 70 BM导致在激发后的前50 ps内的有效PL猝灭。从PL激发实验中没有发现从PCDTBT的HEB向富勒烯受体的直接电子转移的证据,因此可以假设PCDTBT内的内部弛豫机制。我们的研究结果表明,有效的共聚物结构单元之间的耦合支配共混物的光伏性能。

英文摘要:

Donor-acceptor (D-A) type copolymers show great potential for the application in the active layer of organic solar cells. Nevertheless the nature of the excited states, the coupling mechanism and the relaxation pathways following photoexcitation are yet to be clarified. We carried out comparative measurements of the steady state absorption and photoluminescence (PL) on the copolymer poly[N-(1-octylnonyl)-2,7-carbazole] -alt-5,5-[4',7' -di(thien-2-yl)-2',1',3' -benzothiadiazole] (PCDTBT), its building blocks as well as on the newly synthesized N-(1-octylnonyl)-2,7-bis-[(5-phenyl)thien-2-yl)carbazole (BPT-carbazole) (see Figure 1). The high-energy absorption band (HEB) of PCDTBT was identified with absorption of carbazoles with adjacent thiophene rings while the low-energy band (LEB) originates instead from the charge transfer (CT) state delocalized over the aforementioned unit with adjacent benzothiadiazole group. Photoexcitation of the HEB is followed by internal relaxation prior the radiative decay to the ground state. Adding PC70BM results in the efficient PL quenching within the first 50 ps after excitation. From the PL excitation experiments no evidence for a direct electron transfer from the HEB of PCDTBT towards the fullerene acceptor was found, therefore the internal relaxation mechanisms within PCDTBT can be assumed to precede. Our findings indicate that effective coupling between copolymer building blocks governs the photovoltaic performance of the blends.

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