Tuning electronic structures of thiazolo[5,4-d]thiazole-based hole-transporting materials for efficient perovskite solar cells

A solution processable, p-type thiazolo[5,4-d]thiazole-based small organic molecules with appropriate energy levels were employed as hole transport materials (HTMs) in perovskite solar cells (PSCs). The HOMO energy levels of HTMs were tuned to match with methylammonium lead iodide (CH₃NH₃PbI₃) perovskite by incorporating different spacer functional group thiophene, furan, and triphenylamine donor moieties denoted as RTzR (HTM 1), RFTzR (HTM 2) and TPTzR (HTM 3), respectively. The highest power conversion efficiency (PCE) of ~ 10.60% was observed for the PSC fabricated with HTM 2. The other fabricated PSCs with HTM 1 and HTM 3 exhibited inferior PCEs of ~ 4.37% and ~ 8.63% respectively. Noticeably, HTM 2 presented a high fill factor with slightly low open circuit voltage (V_OC) of ~ 0.955 V, which might be related to its low series resistance. Thus, the designed HTM 2 molecule could act as a promising candidate for providing a high efficiency in PSC applications.