Solvent Engineering in Ligand Exchange of the Hole Transport Layer Enables High-Performance PbS Quantum Dot Solar Cells

The performance of lead sulfide colloidal quantum dot (PbS-CQD) solar cells has long been hindered by interface defects in the transport layer. Traditionally, 1,2-ethanedithiol (EDT), used in solid-state ligand exchange, has been a common choice as the hole transport layer (HTL) in many PbS-CQD solar cells. However, the rapid reaction rate and chain length mismatch (shorter-chain EDT versus longer-chain oleic acid) during the ligand exchange process often introduce crack defects in the HTL film, resulting in an unexpected low performance. In this work, ethyl acetate (EA) was introduced into acetonitrile (ACN) solution to slow down the ligand exchange rate. With EA's assistance, a high-quality HTL film with fewer cracks was achieved, leading to a reduced trap density from 2.26 x 1016 cm-3 to 1.85 x 1016 cm-3. Consequently, this led to an improved V OC by 27.5 mV and an increased power conversion efficiency (PCE) from 11.01% to 12.16%.