Improved Charge Carrier Dynamics of CH$_3$NH$_3$PbI$_3$ Perovskite Films Synthesized by Means of Laser-Assisted Crystallization

TL;DR

This study compares laser-assisted and thermal annealing methods for synthesizing CH$_3$NH$_3$PbI$_3$ perovskite films, revealing that laser-assisted crystallization improves grain size and charge transport in certain configurations, enhancing photovoltaic performance.

Contribution

It provides a systematic analysis of how laser irradiation conditions affect perovskite film quality and carrier dynamics, highlighting the benefits and drawbacks of laser-assisted crystallization.

Findings

Laser-assisted process yields larger grains and faster charge extraction in PEDOT:PSS films.

LA process results in slower recombination in PEDOT:PSS structures.

Extensive residual PbI$_2$ in PTAA structures leads to inferior performance.

Abstract

Although it has been recently demonstrated that the laser-assisted (LA) crystallization process leads to the formation of perovskite absorber films of superior photovoltaic performance compared to conventional thermal annealing (TA), the physical origin behind this important discovery is missing. In this study, CH$_3$NH$_3$PbI$_3$ perovskite thin films have been synthesized by means of LA and TA crystallization on the surface of two hole transport layers (HTL) namely poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and poly(triarylamine) (PTAA). A systematic study of the effect of laser irradiation conditions on the crystalline quality and morphology of the perovskite films was performed via scanning electron microscopy, X-Ray diffraction and absorption spectroscopy. Meanwhile, time-resolved transient absorption spectroscopy under inert atmosphere conditions was used to evaluate the carrier transport dynamics. It is found that for the PEDOT:PSS/CH$_3$NH$_3$PbI$_3$, structures the LA process resulted to perovskite layers of larger grains, faster charge carrier extraction properties and slower bimolecular recombination, when compared to TA. On the contrary, the LA-assisted formation of the PTAA/CH$_3$NH$_3$PbI$_3$ heterostructures leads to extensive presence of residual PbI$_2$ and thus inferior performance and charge carrier dynamics.