Suppression of hydroxylation on the surface of colloidal quantum dots to enhance the open-circuit voltage of photovoltaics

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2020-01, Vol.8 (9), p.4844-4849
• Main Authors: Song, Jung Hoon, Kim, Taewan, Park, Taiho, Jeong, Sohee
• Format: Article
• Language: English
• Subjects: Energy conversion efficiency; Fabrication; Hydroxylation; Lead sulfides; Ligands; Open circuit voltage; Optical analysis; Photoelectric effect; Photoelectric emission; Photovoltaic cells; Photovoltaics; Purification; Quantum dots; Solar cells; Sulfide; Surface analysis (chemical); Synthesis; Transient photovoltage; Voltage
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c9ta12598a

The fine control over the surface of lead sulfide colloidal quantum dots (PbS CQDs) is increasingly important to achieve enhanced device performance. In particular, the in-gap trap state resulting from the surface hydroxylation of PbS CQDs is considered detrimental to photovoltaic performance. In this study, we developed a method to avoid hydroxyl formation on the PbS CQD surface by using an in situ solution-phase ligand-exchange process. The complete elimination of protic solvents and other hydroxyl sources from the CQD synthesis to device fabrication produced PbS CQD films without undesired hydroxyl ligands with a reduced trap density. In this process, the purification process, which accounts for nearly 60% of the synthesis cost, is completely excluded. The presence of trap states verified through optical analysis and the hydroxylation observed via surface analysis clearly agreed with the device characterization obtained by transient photovoltage and photocurrent. Consequently, the open-circuit voltage of the PbS CQD solar cells is improved by up to 10%, yielding a certified power-conversion efficiency of 11.6%. Suppression of hydroxylation on quantum dot surfaces demonstrated a solar cell efficiency of 11.6% with the synthesis cost down up to 59.3%.