Enhanced Passivation and Carrier Collection in Ink-Processed PbS Quantum Dot Solar Cells via a Supplementary Ligand Strategy

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Abstract
Solution-processed semiconductors have opened promising avenues for next-generation semiconductor and optoelectronic industries. Colloidal quantum dots (CQDs) as one of the typical materials are widely utilized for the design and development of light emission diodes, photodetectors and solar cells. Recently, an emerging process of PbS QDs-ink has been employed to attain world record power-conversion efficiency (PCE) by surface passivation using a PbI2 ligand to form PbI2-PbS as well as the process optimization in the field of photovoltaics. However, the bonding and debonding of the ligands on the surface of PbS QDs are dynamic reversible processes in an ink environment. The uncoordinated Pb2+ defects induced by un-bonded PbS QDs serve as the recombination sites. Thus, the present ink process leaves much room for the enhancement by surface passivation of PbS QDs. Herein, we devise an efficient strategy with a supplementary phenethylammonium iodide (PEAI) ligand for the formation of the PEAI-PbS interface in PbS QDs ink-processed solar cells. This newly developed method can not only improve the passivation on QDs surface by iodine ions, but also simultaneously enhance the carrier collection efficiency by a graded energy alignment between PbI2-PbS and PEAI-PbS layers. The corresponding power conversion efficiency (PCE) of the optimized device has significantly increased by approximately 20% more than the control device. As a result, such robust and efficient method regarded as a strategic candidate can overcome the bottleneck of imperfect passivation caused by large specific surface area and loose bonding ligands, eventually promoting industrial application of QDs.
Funding Information
  • Ministry of Science and Technology of the People's Republic of China (2016YFB0700702)
  • National Natural Science Foundation of China (21833009, 51761145048, 61874165)
  • Shenzhen Science and Technology Innovation Committee (JCYJ20170413113645633)

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