Applications of lead halide perovskites in solar cells and photo- and ionising radiation detectors are based on effective charge carrier generation and transport. The perovskites exhibit large carrier recombination lifetimes and diffusion coefficients leading to exceptionally long carrier diffusion lengths for solution processed materials. However, carrier density dependences of these parameters are not very well established. Therefore, in this work, we have used non-destructive optical techniques such as time-resolved differential absorption, time-resolved photoluminescence and light induced transient gratings (LITG) for the simultaneous determination of carrier density dependent recombination and diffusion rates as well as diffusion length in MAPbI₃ and MAPBr₃ crystals in a wide range of excitation densities upon single and two photon injections. At low carrier densities, recombination processes on bulk and surface traps were found to be dominant providing 1–2 μs lifetime, and 6 × 10³; ∼30 cm s⁻¹ surface recombination velocities in MAPbI₃ and MAPbBr₃ crystals, respectively. For higher carrier densities, an enhancement in carrier recombination rate as well as an increase in carrier diffusivity is observed. We related the lifetime reduction with excitation to the bimolecular and Auger recombination processes with B₀ = 1.0 (4) × 10⁻¹⁰ cm³ s⁻¹ and C = 1.5 (1.2) × 10⁻²⁹ cm⁶ s⁻¹ coefficients in MAPbI₃ and MAPbBr₃, respectively. The LITG measurements provide a direct increase in the carrier density dependent diffusion coefficient from 1.35 to 3 cm² s⁻¹ in MAPbI₃ and from 0.45 cm² s⁻¹ to 1.7 cm² s⁻¹ in MAPbBr₃ due to the carrier plasma degeneracy and saturation of localized states. A high carrier density related diffusion length drop from 10 to 0.1 μm in the 10¹⁶–10¹⁹ cm⁻³ carrier density range was observed.

中文翻译：

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在单光子激发和双光子激发下测量的MAPbI3和MAPbBr3晶体中依赖于载流子密度的扩散系数，重组率和扩散长度

钙钛矿卤化物在太阳能电池以及光和电离辐射探测器中的应用基于有效的载流子产生和传输。钙钛矿表现出大的载流子复合寿命和扩散系数，导致溶液加工材料的载流子扩散长度特别长。但是，这些参数对载流子密度的依赖性不是很好。因此，在这项工作中，我们使用了无损光学技术，例如时间分辨差分吸收，时间分辨光致发光和光诱导瞬态光栅（LITG），用于同时确定与载流子密度有关的重组和扩散速率以及扩散MAPbI ₃和MAPBr _3中的长度单次和两次光子注入时，晶体的激发密度范围很广。在低载流子密度下，发现在体陷阱和表面陷阱上的重组过程占主导地位，可提供1-2μs的寿命，以及6×10 ³。MAPbI ₃和MAPbBr ₃晶体的表面重组速度分别约为30 cm s ^-1。对于更高的载流子密度，观察到载流子复合率的增加以及载流子扩散率的增加。我们将激发引起的寿命减少与B ₀ = 1.0（4）×10 ^-10 cm ³ s ^-1和C的双分子和俄歇复合过程相关。MAPbI ₃和MAPbBr _3中的系数分别为1.5（1.2）×10 ^-29 cm ⁶ s ^-1。所述LITG测量从1.35至3cm提供在载流子密度依赖性的扩散系数直接增加^2个小号^-1在MAPbI ₃和从0.45厘米^2个小号^-1至1.7厘米^2个小号^-1在MAPbBr ₃由于载流子等离子体的简并性和局部状态的饱和度。与高载流子密度有关的扩散长度在10 ¹⁶ –10 ¹⁹ cm ^-3中从10下降到0.1μm 观察到载流子密度范围。