Colloidal quantum dots (QDs) have garnered significant attention for photovoltaics owing to their unique properties, including size-tunable bandgaps, and multiple exciton generation. Additionally, their simple and controllable synthesis, decoupled crystallization from film deposition, and room-temperature solution processing with green solvents offer a versatile platform for high-throughput processing for large-area optoelectronic applications. However, the introduction of long-chain insulating ligands during synthesis inhibits electronic coupling between perovskite QDs (PeQDs), necessitating time-consuming layer-by-layer (LbL) deposition and solid-state ligand exchange processes, which limits their application in large-area printed optoelectronic devices. Thus, designing and synthesizing stable colloidal PeQD conductive inks, which enhance electronic coupling between QDs while simplifying the film deposition process, is an effective approach compatible with large-area printed optoelectronic devices. However, the soft lattice ionic nature of perovskites and the dynamic surface of PeQDs are susceptible to disruption by polar solvents, resulting to PeQD aggregation and even phase transitions, making the preparation of stable PeQD conductive inks a significant challenge.
To address these challenges, Prof. Jianyu Yuan and Prof. Wanli Ma's team at the Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, developed a sequential acylation-coordination protocol (SACP) to design and synthesize stable PeQD conductive inks. By introducing functional amines (dipropylamine) to acylate with long-chain oleic acid ligands, the oleic acid ligands were removed while utilizing the dynamic binding process on the PeQD surface to induce the desorption of oleylamine ligands. Subsequently, they added a higher affinity Lewis base ligand (triphenylphosphine) soluble in non-polar solvents to passivate defects and enhance the surface stability and dispersibility of the PeQDs. The SACP strategy demonstratedversatility in preparing conductive inks for different PeQD systems (FAPbI3, MAPbI3, CsPbI3). Using the air-stable PeQD inks, the team developed a one-step deposition process for simplifying the PeQD film preparation. The resultant PeQD film displays uniform morphology with elevated electronic coupling, more ordered structure and homogeneous energy landscape compared to LbL films. Ultimately, small-area solar cells based on the narrow-bandgap FAPbI3 PeQD inks achieved a power conversion efficiency (PCE) of 16.61% (certified 16.20%), with a 1 cm² device reaching a PCE of 14.05% and the devices exhibited superior stability. Additionally, the conductive PeQD inks are compatible with large-area device fabrication using the blade-coating technique with a speed up to 50 mm s−1. paves the way for the high-throughput industrial application of PeQDs in deployable and scalable photovoltaics and other optoelectronics. The related research results were published online in Nature Energy (DOI: 10.1038/s41560-024-01608-5).
Figure. Preparation of conductive PeQD inks and photovoltaic device performance
Link to paper: https://www.nature.com/articles/s41560-024-01608-5
Title: Conductive colloidal perovskite quantum dot inks towards fast printing of solar cells
Authors: Xuliang Zhang, Hehe Huang, Chenyu Zhao, Lujie Jin, Chihyung Lee, Youyong Li, Doo-Hyun Ko, Wanli Ma*, Tom Wu & Jianyu Yuan*
Editor: Danting Xiang, Xin Du