Highly Mobile Large Polarons in Black Phase CsPbI3

Elke Debroye,Hai I Wang,Mischa Bonn,Heng Zhang,Maarten B J Roeffaers,Johan Hofkens,Julian A Steele

doi:10.1021/acsenergylett.0c02482

Elke Debroye, Hai I Wang + Show 5 more

Open Access

https://doi.org/10.1021/acsenergylett.0c02482

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Abstract

We report the band-like transport of photogenerated charge carriers within all-inorganic black γ-phase CsPbI3 (γ-CsPbI3) thin films, with local mobilities up to 270 ± 44 cm2V–1s–1 recorded using terahertz (THz) spectroscopy at room temperature. Temperature-dependent, high-frequency photoconductivity measurements indicate that large polaron formation governs charge carrier transport, following the Feynman polaron model. The mobility values derived using THz spectroscopy are nearly 1 order of magnitude higher than that reported for hybrid organic–inorganic lead halide perovskites and approach the theoretical limit for polarons scattering from longitudinal optical (LO) phonons. Our results identify γ-CsPbI3 as a fascinating all-inorganic perovskite semiconductor with high charge carrier mobility for optoelectronics and reveal the effect of polaron formation on charge transport properties.

Highlights

L ow-cost, solution-processable lead halide perovskites (LHPs) have attracted tremendous attention in recent years owing to their superior photovoltaic performance with the reported single-junction solar cell power conversion efficiency beyond 25%
Br, or I) imposes severe thermal and chemical instability, which impedes the practical realization of hybrid LHP-based applications.[7−10] Within this context, cesium-based allinorganic LHPs (e.g., CsPbX3) are promising alternatives for efficient photovoltaics with improved chemical stability.[7,11,12]
On the basis of the analysis, we find that the monomolecular trapping rate is enhanced (∼40 times higher) compared to MAPbI3 samples reported by Herz.[37]

Summary

Reports for Hybrid LHPs

Based on the lifetime inferred from the dynamics and the estimated mobility, the diffusion length of photogenerated polarons exceeds 1 μm (see the SI for more details). This result illustrates the great potential of the γ-. CsPbI3, we conducted a second estimate of the mobility from the amplitude of the OPTP data as exhibited in Figure 1c,d (see SI for more details) This is distinct from the first method, which relies on the dispersion (frequency dependence) of the complex photoconductivity.

■ ACKNOWLEDGMENTS

■ REFERENCES