Lead halide perovskites are used in thin-film solar cells, which owe their high efficiency to the long lifetimes of photocarriers. Various calculations find that a dynamical Rashba effect could significantly contribute to these long lifetimes. This effect is predicted to cause a spin splitting of the electronic bands of inversion-symmetric crystalline materials at finite temperatures, resulting in a slightly indirect band gap. Direct experimental evidence of the existence or the strength of the spin splitting is lacking. Here, we resonantly excite photocurrents in single crystalline (CH3NH3)PbI3 with circularly polarized light to clarify the existence of spin splittings in the band structure. We observe a circular photogalvanic effect, i.e., the photocurrent depends on the light helicity, in both orthorhombic and tetragonal (CH3NH3)PbI3. At room temperature, the effect peaks for excitation photon energies ΔE=110 meV below the direct optical band gap. Temperature-dependent measurements reveal a sign change of the effect at the orthorhombic–tetragonal phase transition, indicating different microscopic origins in the two phases. Within the tetragonal phase, both ΔE and the amplitude of the circular photogalvanic effect increase with temperature. Our findings support a dynamical Rashba effect in this phase, i.e., a spin splitting caused by thermally induced structural fluctuations which break inversion symmetry.

钙钛矿卤化物用于薄膜太阳能电池中，这是由于它们的高效率归因于光载流子的长寿命。各种计算都发现，动态的Rashba效应可能会大大延长这些使用寿命。据预测，这种作用会在有限的温度下引起反转对称晶体材料电子带的自旋分裂，从而导致间接带隙的产生。缺乏自旋分裂的存在或强度的直接实验证据。在这里，我们共振激发单晶的光电流（CH3ñH3）Pb一世3用圆偏振光来澄清带结构中自旋分裂的存在。我们观察到了圆形的光电效应，即在正交晶系和四方晶系中，光电流取决于光螺旋度（CH3ñH3）Pb一世3。在室温下，激发光子能量的作用达到峰值ΔE=110meV低于直接光学带隙。与温度有关的测量结果表明，正交相-四方相变处的符号效应发生了变化，表明这两个相的微观起源不同。在四方相中，两者ΔE圆形光电流效应的幅度随温度而增加。我们的发现支持该阶段的动态Rashba效应，即由热诱导的结构波动引起的自旋分裂，破坏了反演对称性。