Ultrasmooth organic-inorganic perovskite thin-film formation and crystallization for efficient planar heterojunction solar cells.

Wei Zhang,Michael Saliba,Maximilian T Hörantner,Aditya Sadhanala,Samuel D Stranks,Giles E Eperon,Jack A Alexander-Webber,Ulrich Wiesner,Yulin Chen,Shuhua Yao,Henry J Snaith,Antonio Abate,Lara A Estroff,Thomas Stergiopoulos,Sandeep K Pathak,David T Moore,Richard H Friend

doi:10.1038/ncomms7142

Abstract

To date, there have been a plethora of reports on different means to fabricate organic-inorganic metal halide perovskite thin films; however, the inorganic starting materials have been limited to halide-based anions. Here we study the role of the anions in the perovskite solution and their influence upon perovskite crystal growth, film formation and device performance. We find that by using a non-halide lead source (lead acetate) instead of lead chloride or iodide, the perovskite crystal growth is much faster, which allows us to obtain ultrasmooth and almost pinhole-free perovskite films by a simple one-step solution coating with only a few minutes annealing. This synthesis leads to improved device performance in planar heterojunction architectures and answers a critical question as to the role of the anion and excess organic component during crystallization. Our work paves the way to tune the crystal growth kinetics by simple chemistry.

Highlights

To date, there have been a plethora of reports on different means to fabricate organic– inorganic metal halide perovskite thin films; the inorganic starting materials have been limited to halide-based anions
It is noted that we do not use a ratio of 1:1 of CH3NH3I:PbI2 as the focus of this study is to elucidate the role of anions when processed with excess organic component, as we employ in our conventional ‘mixed halide’ perovskite CH3NH3PbI3 À xClx
Since the perovskite does not form at 100 °C from the solution using PbI2 as the lead source, even after 12 h annealing, the temperature was increased to 150 °C for this PbI2 route

Summary

Introduction

There have been a plethora of reports on different means to fabricate organic– inorganic metal halide perovskite thin films; the inorganic starting materials have been limited to halide-based anions. We find that by using a non-halide lead source (lead acetate) instead of lead chloride or iodide, the perovskite crystal growth is much faster, which allows us to obtain ultrasmooth and almost pinhole-free perovskite films by a simple one-step solution coating with only a few minutes annealing. This synthesis leads to improved device performance in planar heterojunction architectures and answers a critical question as to the role of the anion and excess organic component during crystallization. By optimizing device fabrication conditions, we achieve a power conversion efficiency (PCE) of 15.2% in a PHJ architecture through the PbAc2 route, measured under one sun illumination, which is a significant improvement upon similar solar cells fabricated from either PbCl2 or PbI2 routes

Methods

Results

Conclusion