Schulz Matthias, Mack Majvor, Kolloge Oliver, Lützen Arne, Schiek Manuela
Kekulé Institute of Organic Chemistry and Biochemistry, Rheinische-Friedrich-Wilhelms-University of Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany.
Energy and Semiconductor Research Laboratory, Institute of Physics, University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, D-26129 Oldenburg, Germany.
Phys Chem Chem Phys. 2017 Mar 8;19(10):6996-7008. doi: 10.1039/c7cp00306d.
We suggest and explore a novel route towards organic photodetectors sensitive to the circular polarization state of light. For this, we insert fullerene-blended thin films of homochiral squaraine compounds acting as a highly circular dichroic active layer into conventional bulk hetero-junction photodiodes. Initially, we discuss steady-state characterization of photodiodes with unpolarized light. The homochiral, l-proline derived squaraine compounds are obtained via a chiral pool synthesis in sizable quantities. The aggregation behavior of the two compounds with varying side chain length is complex. They exhibit H-type spectral signatures only in colloidal solution, and both H- and J-type features with large splitting in neat and fullerene-blended thin films. We probe strong excitonic circular dichroism for both aggregate species, showing the most competitive dissymmetry factors up to -0.055 in fullerene-blended thin films. We vary the blend ratio and layer thickness of such active layers in the photodiodes. The device performance is in all cases limited by a low fill factor which is accompanied by a voltage-dependent photocurrent. Current-voltage measurements show light intensity dependent characteristics, which are S-shaped, contrary to our expectations, only for thin active layers independent of the blend ratio. The external quantum efficiency is in some cases extraordinarily high, exceeding 100 percent in the blue spectral range under modest reverse bias voltages for thin, fullerene-rich devices. However, the most promising are the devices with thick, donor-rich layers defined by a spectral overlap of the strongest photocurrent response and the maximum circular dichroism within the green spectral range. Thus, we demonstrate the feasibility of combining photodiode functionality and strong circular dichroism as intrinsic material properties.
我们提出并探索了一条通往对光的圆偏振态敏感的有机光电探测器的新途径。为此，我们将作为高度圆二色性活性层的手性纯方酸化合物与富勒烯混合的薄膜插入传统的体异质结光电二极管中。首先，我们讨论了非偏振光下光电二极管的稳态特性。手性纯的、由L-脯氨酸衍生的方酸化合物通过手性池合成大量获得。两种侧链长度不同的化合物的聚集行为很复杂。它们仅在胶体溶液中表现出H型光谱特征，而在纯的和与富勒烯混合的薄膜中都表现出具有大分裂的H型和J型特征。我们探测了两种聚集物种的强激子圆二色性，在与富勒烯混合的薄膜中显示出高达-0.055的最具竞争力的不对称因子。我们改变了光电二极管中这种活性层的混合比例和层厚度。在所有情况下，器件性能都受到低填充因子的限制，同时伴随着与电压相关的光电流。电流-电压测量显示出光强度依赖特性，与我们的预期相反，仅对于与混合比例无关的薄活性层呈S形。在某些情况下，外部量子效率非常高，对于薄的、富富勒烯的器件，在适度的反向偏置电压下，在蓝色光谱范围内超过100%。然而，最有前景的是具有厚的、富施主层的器件，其由最强光电流响应的光谱重叠和绿色光谱范围内的最大圆二色性定义。因此，我们证明了将光电二极管功能和强圆二色性作为固有材料特性相结合的可行性。
