Low-Bandgap Donor/Acceptor Polymer Blend Solar Cells with Efficiency Exceeding 4%
Low-Bandgap Donor/Acceptor Polymer Blend Solar Cells with Efficiency Exceeding 4%
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DOI：
10.1002/aenm.201301006
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发表时间：
2014-02-01
影响因子：
27.8
通讯作者：
Ito, Shinzaburo
中科院分区：
文献类型：
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作者：
Mori, Daisuke;Benten, Hiroaki;Ito, Shinzaburo
共轭聚合物太阳能电池作为一种可能的廉价可再生能源而受到越来越多的关注，因为其具有高吞吐量和采用低成本印刷工艺进行大面积生产等优点。 [1]研究最多的基于聚合物的太阳能电池具有本体异质结（BHJ）活性层，其中电子供体（D）聚合物与低分子量富勒烯衍生物的受体（A）混合。聚合物/富勒烯BHJ太阳能电池的功率转换效率（PCE）在过去十年中稳步提高。[2-5]另一方面，由聚合物供体和受体组成的聚合物/聚合物BHJ也成为了积极研究的主题，因为它比传统聚合物/富勒烯系统具有许多潜在优势。[6]特别是，D 和 A 聚合物的灵活分子设计为调节材料的光学、电子和形态特性提供了很大的空间。例如，D 和 A 聚合物的混合物在可见光和近红外波长范围内具有高吸收系数，能够捕获大部分太阳光，从而产生较大的短路电流密度 (JSC)。此外，调整D和A聚合物的最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）水平将使开路电压（VOC）升至1 V以上。此外，相分离的互穿聚合物形态将为电荷载流子传输提供连续的路径，从而实现高填充因子（FF）。然而，尽管有这些吸引人的特点，聚合物/聚合物 BHJ 太阳能电池的 PCE 仍保持在约 2%，[7-9] 远远落后于聚合物/富勒烯 BHJ 太阳能电池的效率。 [10]立体规则性聚(3-己基噻吩)(P3HT)是聚合物/聚合物BHJ太阳能电池中最广泛使用的供体聚合物之一，因为晶体中的π−π链间堆积使其具有优异的空穴迁移率。然而，无论用作受体的聚合物的性质如何，P3HT/受体聚合物 BHJ 太阳能电池的外部量子效率 (EQE) 均低于 30%。[8, 11–13] 这些值与 P3HT/富勒烯系统显示的 70% 至 80% 的 EQE 显着不同。[4]迄今为止报道的聚合物/聚合物BHJ太阳能电池较差的PCE主要归因于共混物的不良形貌，例如大相分离域尺寸、不均匀的内相组成和结晶度降低。[6-8,11,13-15]因此，一些研究人员尝试通过热退火[7,8]和/或使用溶剂添加剂[12]和供体-受体二嵌段来控制相分离的纳米级结构共聚物。[16]最近，通过使用P3HT作为供体和高分子量芴基共聚物（PF12TBT）作为受体，PCE达到了2.7%。 [7]在此报告的研究中，我们利用聚[2, 3-双-(3-辛氧基苯基)喹喔啉-5, 8-二基-替代噻吩-2, 5-二基](PTQ1)[17]作为聚合物/聚合物BHJ太阳能电池中的供体聚合物（图1a）。如图 1c 所示，PTQ1 表现出更长的吸收边（高达 700 nm）和以 630 nm 为中心的分子内电荷转移吸收带，与 P3HT 相比，在长波长下具有更有效的光吸收。此外，即使在非晶相中，PTQ1薄膜在BHJ结构中也表现出足够的空穴传输[17]，这将消除控制结晶的困难。聚{[N,N'-双(2-辛基十二烷基)-萘-1,4,5,8-双(二甲酰亚胺)-2,6-二基]-alt-5,5'-(2,2'-联噻吩)}[P(NDI2OD-T2); PolyeraActivInk N2200][18 …
Conjugated polymer-based solar cells have gained increasing attention as a possible inexpensive source of renewable energy because of their advantages including high throughput and large-area production with low-cost printing processes.[1] The most studied polymer-based solar cells have a bulk-heterojunction (BHJ) active layer in which an electron donor (D) polymer is mixed with an acceptor (A) of low molecular weight fullerene derivative. The power-conversion efficiency (PCE) of the polymer/fullerene BHJ solar cells has steadily increased over the last ten years.[2–5] On the other hand, polymer/polymer BHJs consisting of a polymeric donor and acceptor have also been a subject of active research because of a number of potential advantages over conventional polymer/fullerene systems.[6] In particular, the flexible molecular design of both D and A polymers affords large scope for tuning the optical, electronic, and morphological properties of the materials. For instance, the blends of D and A polymers with high absorption coefficients in the visible and near-infrared ranges of wavelengths are able to harvest a large portion of sun light to yield a large short-circuit current density (JSC). Furthermore, the adjustment of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the D and A polymers will allow the open-circuit voltage (VOC) to rise above 1 V. In addition, the phase-separated interpenetrating polymer morphologies will offer continuous pathways for charge-carrier transport, leading to a high fill factor (FF). However, despite these attractive features, the PCE of polymer/polymer BHJ solar cells remains at≈ 2%,[7–9] lagging far behind the efficiency of polymer/fullerene BHJ solar cells.[10] Regioregular poly (3-hexylthiophene)(P3HT) is one of the most widely used donor polymers in the polymer/polymer BHJ solar cells because of its excellent hole mobility owing to the π− π interchain stacking in crystals. However, the external quantum efficiencies (EQEs) reported for the P3HT/acceptorpolymer BHJ solar cells are below 30% regardless of the nature of the polymers used as acceptors.[8, 11–13] These values are significantly different from the EQEs ranging from 70 to 80% shown by the P3HT/fullerene systems.[4] The poor PCEs of polymer/polymer BHJ solar cells reported so far are mainly attributed to the undesirable morphology of the blends such as large phase-separated domain sizes, inhomogeneous internal phase composition, and reduced crystallinity.[6–8, 11, 13–15] Therefore, some researchers attempt to control the nanoscale structure of phase separation by thermal annealing [7, 8] and/or by using solvent additives [12] and donor− acceptor diblock copolymers.[16] Recently, a PCE of 2.7% has been achieved by using P3HT as a donor and a high molecular weight fluorene-based copolymer (PF12TBT) as an acceptor.[7] In the study reported here, we utilized poly [2, 3-bis-(3-octyloxyphenyl) quinoxaline-5, 8-diyl-alt-thiophene-2, 5-diyl](PTQ1)[17] as a donor polymer in polymer/polymer BHJ solar cells (Figure 1 a). As shown in Figure 1 c, PTQ1 exhibited a longer absorption edge to up to≈ 700 nm and an intramolecular charge transfer absorption band centered at 630 nm, leading to more efficient light absorption at long wavelengths compared to P3HT. Moreover, PTQ1 films showed sufficient hole transport in the BHJ structures [17] even in the amorphous phase, which would eliminate the difficulties in controlling the crystallization. Poly {[N, N′-bis (2-octyldodecyl)-naphthalene-1, 4, 5, 8-bis (dicarboximide)-2, 6-diyl]-alt-5, 5′-(2, 2′-bithiophene)}[P (NDI2OD-T2); PolyeraActivInk N2200][18 …