Decoupling engineering of formamidinium–cesium perovskites for efficient photovoltaics

High-efficiency formamidinium-cesium triiodide perovskites photovoltaics
(a) Schematic diagram of the SCI-FA1-xCsxPbI3 perovskite films fabricated by decoupling the crystallization process of formamidinium and cesium. (b) 3D distribution of Cs+ in the SCI-FA0.91Cs0.09PbI3 and 1S-FA0.91Cs0.09PbI3 film by ToF-SIMS analysis. (c) The J-V curves of the champion solar cell devices based on FAPbI3, SCI-FA0.91Cs0.09PbI3 and 1S-FA0.91Cs0.09PbI3 perovskites. Credit: Science China Press

Metal halide perovskites (ABX3) have emerged as promising candidates for various optoelectronic applications due to their excellent optoelectronic properties and low-cost fabrication. At present, the light-absorbing layer of the highest-efficiency single-junction perovskite solar cells (PSCs) is almost all based on FAPbI3 perovskite, achieving power conversion efficiency (PCE) that is comparable to commercial crystalline silicon cells.

However, the photoactive black-phase FAPbI3 readily transforms to a photo-inactive yellow phase under humid conditions. Composition engineering such as A/X-site alloying has been developed to stabilize the black-phase FAPbI3.

Notably, alloying FA+ with Cs+ to formpure-iodide FA-Cs (FA1-xCsxPbI3) is an ideal approach to obtain PSCs with and stability. However, due to the complex crystallization kinetics between FAPbI3 and CsPbI3, FA1-xCsxPbI3 perovskite prepared by typical one-step (1S) crystallization exhibits poor compositional homogeneity and high trap density, which limits the device performance and long-term stability.

To tackle this challenge, Professor Yixin Zhao from Shanghai Jiao Tong University and co-workers recently developed a strategy of sequential cesium incorporation (SCI) to decouple the crystallization of FA-Cs triiodide perovskite with highly efficient and stable PSCs achieved.

In this work, cesium formate (HCOOCs) as a cesium source is sequentially introduced into high-quality FA precursor film. By cooperating with Professor Feng Gao from Linköping University, a new stabilization mechanism for Cs doping to stabilize FAPbI3 is also revealed. This research article is published in National Science Review.

In their work, high-quality FA1-xCsxPbI3 (x=0.05-0.16) perovskites are obtained by the SCI method. The ratio of FA to Cs in these SCI-FA1-xCsxPbI3 perovskites can be facilely tuned by adjusting the content of the cesium source.

Compared with the conventional one-step-prepared 1S-FA1-xCsxPbI3 perovskites, SCI-FA1-xCsxPbI3 perovskites have demonstrated a much more uniform Cs distribution. "The uniform composition distribution of Cs is the key to the enhancement of device performance," Zhao says, while the PSCs based on SCI-FA0.91Cs0.09PbI3 films achieved a PCE of 24.7% (certified 23.8%), which is the highest value among the FA-Cs triiodide PSCs reported so far.

Moreover, the collaboration with Gao's group further revealed a new stabilization mechanism for this Cs doping. The incorporation of Cs into FAPbI3 significantly reduces the electron-phonon coupling strength and lattice fluctuation, thereby suppressing ionic migration and the formation of iodide-rich clusters. As a result, the stability of FA-Cs based devices has been greatly improved.

Overall, this work opens up new possibilities to strategically develop high-quality mixed-cation perovskites with good control over the crystallization kinetics, presenting a milestone towards the rational construction of highly efficient and stable perovskite-based optoelectronic applications, including but not limited to , , and lasers.

More information: Haoran Chen et al, Decoupling engineering of formamidinium–cesium perovskites for efficient photovoltaics, National Science Review (2022). DOI: 10.1093/nsr/nwac127

Citation: Decoupling engineering of formamidinium–cesium perovskites for efficient photovoltaics (2022, September 16) retrieved 8 December 2023 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Explore further

Solvent effect on film formation and device performance for 2D Dion-Jacobson perovskite solar cells


Feedback to editors