Crystal‐Size‐Induced Band Gap Tuning in Perovskite Films

Amita Ummadisingu,Alessandro Mattoni,Wolfgang Tress,Simone Meloni,Michael Grätzel

doi:10.1002/ange.202106394

Abstract

AbstractA comprehensive picture explaining the effect of the crystal size in metal halide perovskite films on their opto‐electronic characteristics is currently lacking. We report that perovskite nanocrystallites exhibit a wider band gap due to concurrent quantum confinement and size dependent structural effects, with the latter being remarkably distinct and attributed to the perturbation from the surface of the nanocrystallites affecting the structure of their core. This phenomenon might assist in the photo‐induced charge separation within the perovskite in devices employing mesoporous layers as they restrict the size of nanocrystallites present in them. We demonstrate that the crystal size effect is widely applicable as it is ubiquitous in different compositions and deposition methods employed in the fabrication of state‐of‐the‐art perovskite solar cells. This effect is a convenient and effective way to tune the band gap of perovskites.

Highlights

Perovskite materials have recently emerged as excellent candidates for opto-electronic applications, photovoltaics in particular
We demonstrate that the crystal size effect we have described above for methylammonium lead iodide is clearly observed for this complex triple-cation composition deposited via the anti-solvent method
Our study demonstrates that methylammonium lead iodide perovskite films exhibit a blue-shift in the PL spectra and the presence of an asymmetry in the emission during formation in the sequential deposition method, attributed to small perovskite nanocrystallites which are present at the early stages of the reaction

Summary

Introduction

Perovskite materials have recently emerged as excellent candidates for opto-electronic applications, photovoltaics in particular. Perovskite solar cells have been developed in a variety of architectures, including the mesoscopic,[2] planar[3] and inverted ones.[4] The state-of-the-art mesoscopic cells[2] are based on a mesoporous layer of TiO2 particles, which serves as the electron transport layer. Such cells consist of a capping layer of perovskite crystals on top of the mesoscopic TiO2 layer, which is itself infiltrated with perovskite. Planar architectures consist only of a compact perovskite layer between electron and hole transport layer,[5] with the simpler architecture presenting its own advantages

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