Optimizing Surface Chemistry of PbS Colloidal Quantum Dot for Highly Efficient and Stable Solar Cells via Chemical Binding

• Published in: Advanced science Vol. 8; no. 2; pp. 2003138 - n/a
• Main Authors: Hu, Long, Lei, Qi, Guan, Xinwei, Patterson, Robert, Yuan, Jianyu, Lin, Chun‐Ho, Kim, Jiyun, Geng, Xun, Younis, Adnan, Wu, Xianxin, Liu, Xinfeng, Wan, Tao, Chu, Dewei, Wu, Tom, Huang, Shujuan
• Format: Journal Article
• Language: English
• Published: Germany John Wiley & Sons, Inc 01.01.2021; John Wiley and Sons Inc; Wiley
• Subjects: Bands; chemical binding; Communication; Communications; Efficiency; Fourier transforms; Iodine; Ligands; PbS colloidal quantum dots; Photovoltaic cells; Quantum dots; solar cells; Surface chemistry; surface chemistry; solar cells; PbS colloidal quantum dots; chemical binding
• ISSN: 2198-3844; 2198-3844
• DOI: 10.1002/advs.202003138

The surface chemistry of colloidal quantum dots (CQD) play a crucial role in fabricating highly efficient and stable solar cells. However, as‐synthesized PbS CQDs are significantly off‐stoichiometric and contain inhomogeneously distributed S and Pb atoms at the surface, which results in undercharged Pb atoms, dangling bonds of S atoms and uncapped sites, thus causing surface trap states. Moreover, conventional ligand exchange processes cannot efficiently eliminate these undesired atom configurations and defect sites. Here, potassium triiodide (KI3) additives are combined with conventional PbX2 matrix ligands to simultaneously eliminate the undercharged Pb species and dangling S sites via reacting with molecular I2 generated from the reversible reaction KI3 ⇌ I2 + KI. Meanwhile, high surface coverage shells on PbS CQDs are built via PbX2 and KI ligands. The implementation of KI3 additives remarkably suppresses the surface trap states and enhances the device stability due to the surface chemistry optimization. The resultant solar cells achieve the best power convention efficiency of 12.1% and retain 94% of its initial efficiency under 20 h continuous operation in air, while the control devices with KI additive deliver an efficiency of 11.0% and retains 87% of their initial efficiency under the same conditions. Ligand exchange is performed on PbS colloidal quantum dots using conventional PbX2 ligands and KI3 additives via a facile one‐step process, which simultaneously eliminate the undesirable sites and efficiently passivate the surface. The resulting solar cells achieve a power conversion efficiency of 12.1%.