Abstract
Six novel organic small molecules, TPA-Sp-PA (1), TPA-Sp-PE (1E), TPA-T-PA (2), TPA-T-PE (2E), TPA-P-PA (3) and TPA-P-PE (3E) are developed and applied to NiOx films as self-assembled monolayers (SAMs) for tin perovskite solar cells (TPSCs). The linker between acceptor (phosphonic acid (PA) or phosphonic ester (PE)) and donor (triphenylamine (TPA)) plays an important role in facilitating the growth of high-quality perovskite films using a two-step method. Three different types of linkers, phenyl ring (P), thiophene (T), and selenophene (Sp), are studied, for which the Sp-based SAMs provide the best device performance with TPA-Sp-PE (1E) achieving a PCE 8.7%, and its acidic analog, TPA-Sp-PA (1), reaching a maximum PCE of 8.3%. Single crystal structures of TPA-Sp-PE (1E) and TPA-T-PE (2E) are successfully obtained, with the expectation that a uniform SAM would form on the NiOx/ITO substrate. The research introduces a novel approach to enhance TPSC performance by integrating organic SAMs with NiOx HTMs, offering a promising avenue for future progress in TPSC technology through a two-step fabrication technique.