Crystalline versus Amorphous Donor-Acceptor Blends: Influence of Layer Morphology on the Charge-Transfer Density of States
Crystalline versus Amorphous Donor-Acceptor Blends: Influence of Layer Morphology on the Charge-Transfer Density of States
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DOI：
10.1103/physrevapplied.13.024061
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发表时间：
2020-02
影响因子：
4.6
通讯作者：
Theresa Linderl;T. Zechel;A. Hofmann;Tomoya Sato;K. Shimizu;H. Ishii;W. Brütting
中科院分区：
文献类型：
--
作者：
Theresa Linderl;T. Zechel;A. Hofmann;Tomoya Sato;K. Shimizu;H. Ishii;W. Brütting
以有机小分子太阳能电池为实验平台，研究了薄膜形貌对电荷转移态密度的影响。CT态被认为是有机供体-受体太阳能电池中电荷产生的前体，其能量是开路电压的上限。在这项研究中，形态的影响，为两个苝捐助者[结晶二茚苝（DIP）与无定形四苯基二苯并periflanthene（DBP）]具有几乎相同的电离能进行了研究。作为受体材料，使用富勒烯C60。通过将器件测量与光学和低能紫外光电子能谱相结合，获得了一个全面的图像，描述了形态和连接态密度（DOS）如何影响器件性能和CT状态的光谱特征。特别是对于晶体施主材料DIP，观察到远到达差距的强指数尾态，这可能与晶界的存在有关。这些状态的电压依赖性填充被确定为随着施加电压的增加的电致发光光谱的蓝移的起源。比较了不同的方法，研究了静态和动态无序对有机太阳能电池CT发射和吸收光谱描述的影响。尽管两个供体产生几乎相同的CT能量（并且因此产生相同的开路电压），但光电流和电致发光光谱之间的斯托克斯位移以及伴随的CT DOS的宽度变化超过2倍。我们讨论了这一观察方面的donoracceptor重组能量，以及一个额外的线加宽的静态无序。值得注意的是，更多的结晶供体DIP显示出显着偏离马库斯型描述，而这不是无定形DBP的情况。这突出了薄膜形态在有机太阳能电池中的重要性。
Organic small molecule solar cells are used as a test bed to investigate the influence of film morphology on the density of charge-transfer (CT) states. CT states are considered as precursors for charge generation and their energy as the upper limit for the open-circuit voltage in organic donor-acceptor solar cells. In this study the influence of morphology for two perylene donors [crystalline diindenoperylene (DIP) versus amorphous tetraphenyldibenzoperiflanthene (DBP)] with almost identical ionization energy is investigated. As acceptor material, the fullerene C60 is used. By combining device measurements with optical and low-energy ultraviolet photoelectron spectroscopy, a comprehensive picture is obtained that describes how morphology and the connected density of states (DOS) affect device performance and the spectroscopic signature of CT states. Especially for the crystalline donor material DIP, strong exponential tail states reaching far into the gap are observed, which can be related to the presence of grain boundaries. A voltage-dependent filling of these states is identified as the origin of a blue shift of electroluminescence spectra with increasing applied voltage. Different approaches are compared to study the influence of static and dynamic disorder in the description of CT emission and absorption spectra of organic solar cells. Despite the fact that both donors yield almost identical CT energy (and, thus, the same open-circuit voltage) the Stokes shift between photocurrent and electroluminescence spectra and, concomitantly, the width of the CT DOS varies by more than a factor of 2. We discuss this observation in terms of the donoracceptor reorganization energy as well as an additional line broadening by static disorder. Remarkably, the more crystalline donor DIP shows a significant deviation from a Marcus-type description, while this is not the case for the amorphous DBP. This highlights the importance of film morphology in organic solar cells.