Bokdam Menno, Sander Tobias, Stroppa Alessandro, Picozzi Silvia, Sarma D D, Franchini Cesare, Kresse Georg
University of Vienna, Faculty of Physics and Center for Computational Materials Science, Sensengasse 8/12, 1090 Vienna, Austria.
Consiglio Nazionale delle Ricerche - CNR-SPIN, I-67100 L' Aquila, Italy.
Sci Rep. 2016 Jun 28;6:28618. doi: 10.1038/srep28618.
The development of high efficiency perovskite solar cells has sparked a multitude of measurements on the optical properties of these materials. For the most studied methylammonium(MA)PbI3 perovskite, a large range (6-55 meV) of exciton binding energies has been reported by various experiments. The existence of excitons at room temperature is unclear. For the MAPbX3 perovskites we report on relativistic Bethe-Salpeter Equation calculations (GW-BSE). This method is capable to directly calculate excitonic properties from first-principles. At low temperatures it predicts exciton binding energies in agreement with the reported 'large' values. For MAPbI3, phonon modes present in this frequency range have a negligible contribution to the ionic screening. By calculating the polarization in time from finite temperature molecular dynamics, we show that at room temperature this does not change. We therefore exclude ionic screening as an explanation for the experimentally observed reduction of the exciton binding energy at room temperature and argue in favor of the formation of polarons.
高效钙钛矿太阳能电池的发展引发了对这些材料光学性质的大量测量。对于研究最多的甲基铵（MA）PbI₃钙钛矿，各种实验报道了激子结合能的大范围（6 - 55 meV）。室温下激子的存在尚不清楚。对于MAPbX₃钙钛矿，我们报道了相对论性贝特 - 萨尔皮特方程计算（GW - BSE）。这种方法能够从第一性原理直接计算激子性质。在低温下，它预测的激子结合能与报道的“大”值一致。对于MAPbI₃，这个频率范围内存在的声子模式对离子屏蔽的贡献可以忽略不计。通过从有限温度分子动力学计算时间上的极化，我们表明在室温下情况不会改变。因此，我们排除离子屏蔽作为室温下实验观察到的激子结合能降低的一种解释，并支持极化子的形成。
