Additive‐Assisted Crystallization Dynamics in Two‐Step Fabrication of Perovskite Solar Cells

Abstract

Perovskite absorber layers for thin‐film solar cells can be fabricated by a variety of methods including solution‐ and vacuum‐based methods. Solution‐processed perovskite thin‐films prepared by two‐step methods often suffer from small grains and thus reduced optoelectronic performance. In this work, a simple and universal way to control the crystallization dynamics of perovskite (CH3NH3PbI3) layers prepared by thermal evaporation of lead iodide and a subsequent solution‐based conversion in methylammonium iodide solution is presented. By adding small concentrations of the non‐toxic additive hypophosphorous acid (HPA) in the second fabrication step, a facile way to maintain improved morphology and high quality perovskite films with large crystal size and low number of pin‐holes is demonstrated. Therefore, this approach provides an additional handle to influence the structural properties of perovskite films. In this study, the improved morphology results in an overall increase in power conversion efficiency from 5.1% to 8.0%. The additive‐assisted control of crystallization dynamics in perovskite layers is shown to be suitable both for small area deposition techniques, like spin‐coating, as well as large scale deposition techniques, such as inkjet printing. Moreover, it is validated that the additive improves the crystallization on a large variety of substrate materials as well as in ambient and inert process environments.

Secondary Ion Mass Spectrometry (SIMS) for Chemical Characterization of Metal Halide Perovskites

“…A similar phenomenon of the residue Cl − at the bottom of the FA-based perovskite film due to the decreased level of FAI saturation was also discovered by Leyden et al [53] In addition to Br − and Cl − , I − inhomogeneity was also found by Abzieher et al using ToF-SIMS. [54] The authors added a small amount of hypophosphorous acid (HPA) in the MAI solution to control the crystallization dynamics of MAPbI 3 perovskite prepared by a sequential deposition method. ToF-SIMS depth profiles show the obvious phosphoric compound distributed at the interface of perovskite and titania (Figure 8a).…”

“…Reproduced with permission. [54] Copyright 2017, Wiley-VCH. b) ToF-SIMS 2D images showing the distribution of Br − and I − in perovskite films without the addition of Cs + and Rb + (top row), with only Cs + addition (second row), with only Rb + addition (third row), with both Cs + and Rb + addition (bottom row).…”

Coated and Printed Perovskites for Photovoltaic Applications

“…[26,27] In most cases, the desirable morphology of the perovskite thin-film features a large grain size, a dense film (exhibiting as few pinholes as possible), and a low surface roughness. [29] These strategies, which also play an important role for the coating and printing techniques discussed below, include: a) solvent engineering also called ink formulation engineering, [30][31][32][33][34][35][36] a method that combines solvents of different boiling points to control the solvent evaporation and in turn the crystallization; b) additives [37][38][39][40] in the precursor ink to initiate the crystallization of the perovskite thin-film; c) engineering the composition of the precursor materials to impact the crystallization dynamics (through one-step and two-step deposition routes) [8,10,28,41] ; d) solvent quenching, [8,[42][43][44] by adding so-called antisolvents to the wet film that rapidly remove the ink solvent from the wet film and initiate a prompt crystallization; e) vacuum solvent extraction, similarly using vacuum extraction of the ink solvent from the wet film to prompt crystallization [32,45] ; and f) gas quenching [46,47] and gas drying, [48][49][50] again to push out the solvent from the wet film and assist with rapid crystallization. [7,28] Using the low-throughput, but laboratory-friendly, spin-coating technique, strategies to foster the formation of such high-quality perovskite thin-films have been extensively documented in literature.…”

Advances in Inkjet‐Printed Metal Halide Perovskite Photovoltaic and Optoelectronic Devices

“…For hypophosphorous acid (HPA), PbHPO 3 colloids are forming in a reaction cascade of HPA with HI, MA, and PbX 3 , which act as nucleation centers in the perovskite ink. [100][101][102][103] A similar behavior is found for 5-ammoniumvaleric acid (5-AVA), forming a template structure for the perovskite growth. [104] On the contrary, hydrohalic acids such as HI, HBr, and HCl increase the solubility of dissolved lead(II) species, [105] thereby triggering the dissolution of plumbate colloids.…”