Li Jiantao, Wu Ting, Zhang Jia, Haacke Stefan, Teng Feng, Hu Bin
Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States.
College of Science, Beijing Jiaotong University, Beijing 100044, China.
ACS Appl Mater Interfaces. 2020 Aug 26;12(34):38054-38060. doi: 10.1021/acsami.0c09276. Epub 2020 Aug 17.
Hybrid perovskites are known as electrically polarizable semiconductors based on theoretical prediction and experimental information. Here we show the light polarization effects on the photovoltaic actions in perovskite solar cells by optically generating directional and random electronic transition dipoles within asymmetric and symmetric unit structures. In an asymmetric tetragonal unit structure, we observed the stripes with different orientations onto perovskite grains and that the randomly polarized photoexcitation can generate a higher photocurrent (sc) by 6.5 ± 0.5% as compared to the linearly polarized photoexcitation at same intensity in the hysteresis-free perovskite solar cells [ITO/PEDOT:PSS/MAPbI/PCBM/PEI/Ag]. Clearly, switching the photoexcitation between linear and random polarizations leads to a Δsc, which provides an experimental indication that all-directional and one-directional transition dipoles generate higher and lower photocurrents in organic-inorganic hybrid perovskites (MAPbI) with an asymmetric tetragonal unit structure. This implies that all-directional and one-directional transition dipoles develop stronger and weaker dissociative interactions, consequently giving rise to more and less dissociation toward generating photocurrent. This is confirmed by the experimental observation that the Δsc almost disappears when the temperature increases up to 55 °C, where the asymmetric tetragonal structure is changed to a symmetric cubic structure. Furthermore, the Δsc is shown to decrease with increasing light intensity. This indicates that the electronic transition dipoles encounter a polarization relaxation caused by mutual interaction. We show that the polarization relaxation time in MAPbI is comparable to exciton dissociation time (∼ps). This presents the necessary condition to demonstrate light polarization effects of photovoltaic actions in perovskite solar cells.
基于理论预测和实验信息，杂化钙钛矿被认为是可电极化的半导体。在此，我们通过在不对称和对称单元结构内光学产生定向和随机电子跃迁偶极子，展示了光极化对钙钛矿太阳能电池光伏作用的影响。在不对称四方单元结构中，我们观察到钙钛矿晶粒上具有不同取向的条纹，并且在无滞后的钙钛矿太阳能电池[ITO/PEDOT:PSS/MAPbI/PCBM/PEI/Ag]中，与相同强度的线偏振光激发相比，随机偏振光激发可产生高6.5±0.5%的光电流(sc)。显然，在线偏振和随机偏振之间切换光激发会导致Δsc，这提供了一个实验迹象，即全向和单向跃迁偶极子在具有不对称四方单元结构的有机-无机杂化钙钛矿(MAPbI)中产生更高和更低的光电流。这意味着全向和单向跃迁偶极子发展出更强和更弱的解离相互作用，从而导致产生光电流的解离或多或少。当温度升高到55°C时，不对称四方结构变为对称立方结构，此时Δsc几乎消失，这一实验观察结果证实了这一点。此外，Δsc显示出随光强度增加而减小。这表明电子跃迁偶极子遇到了由相互作用引起的极化弛豫。我们表明，MAPbI中的极化弛豫时间与激子解离时间(∼ps)相当。这为证明钙钛矿太阳能电池中光伏作用的光极化效应提供了必要条件。
