Harnessing Functionalized Thioalkylated-Cyclopentadithiophene Monolayers on NiOx for Two-Step Fabricated Tin Perovskite Solar Cells.

A new series of dithioalkylated-methylidenyl-cyclopentadithiophene (CDTS)-based self-assembled monolayers (SAMs), including CDTS-MN (1), CDTS^b-MN (1b), CDTS-CA (2), and CDTS-PA (3), are developed for tin perovskite solar cells (TPSCs). Each SAM incorporates sulphur rich center CDTS and is complemented with various anchoring groups, such as methylenemalononitrile, cyanoacrylic acid, and cyano-vinyl-phosphonic acid in driving the formation of well-crystallized and homogeneous perovskite layers using a two-step fabrication process. Nickel Oxide (NiOx) combined with the newly designed CDTS-based SAMs is utilized as the hole transport material (HTM). This configuration yielded an excellent power conversion efficiency (PCE) of 8.41% for CDTS-MN (1) TPSC device as compared to CDTS^b-MN (1b; PCE: 8.03%), CDTS-CA (2; PCE: 4.54%) and CDTS-PA (3; PCE: 5.15%). Notably, single-crystal structures of CDTS-MN (1) and CDTS^b-MN (1b) are successfully obtained and systematically presented, demonstrating the uniformity of the CDTS monolayers formed on the ITO/NiOx substrate. The CDTS-based SAM 1 excels in TPSCs by enhancing charge transfer and reducing interface recombination through strong π-π stacking and intermolecular S-S interactions. This report highlights the pioneering use of CDTS-based organic sensitizers in TPSCs, representing the first documented application of CDTS-based SAMs within the solar cell research field.