Manipulation of Phase-Transfer Ligand-Exchange Dynamics of PbS Quantum Dots for Efficient Infrared Photovoltaics

• Published in: Journal of physical chemistry. C 2019-12, Vol.123 (50), p.30137-30144
• Main Authors: Wang, Lei, Wang, Yinglin, Jia, Yuwen, Liu, Xinlu, Liu, Ting, Fu, Ting, Li, Jinhuan, Weng, Binbin, Zhang, Xintong, Liu, Yichun
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.9b09231

Chemical surface treatment of colloidal quantum dots (CQDs) by phase-transfer ligand-exchange (PTLE) is essential to implement highly densified, well-passivated CQD films for optoelectronic applications, such as infrared photovoltaics, light-emitting diodes, and photodetectors. PTLE, however, involves parallel and interactional processes of ligand exchange, phase transfer, and surface passivation of CQDs, which render the optimization of PTLE still challenging. Herein, we explored the action mechanism of a widely used additive, ammonium acetate (AA), on the PTLE of PbS CQDs to recognize the dynamic balance during the PTLE process and its impact on the performance of colloidal quantum dot solar cells (CQDSCs). Our research definitely shows that the AA additive can modify the dynamics of PTLE by participating in all of the three processes, and the amount of AA significantly influences the defect passivation and colloidal stability of PbS CQDs. At an appropriate concentration (∼50 mM) of AA, PbS CQDs are well iodide-passivated by PTLE, and the fabricated CQDSCs achieve a power conversion efficiency (PCE) of ∼10% associated with improved carrier transport and reduced trap-assisted carrier recombination. However, excessive AA causes trace residual AA on the CQD surface, resulting in the insufficient surface passivation of PbS CQDs and trap issues of CQDSCs. The double-edged sword effect of the AA additive on PTLE, demonstrated in our work, suggests that realizing a dynamic balance of different processes during PTLE is crucial for further performance promotion of CQDSCs.