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 similar to 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 similar to 4.37% and similar to 8.63% respectively. Noticeably, HTM 2 presented a high fill factor with slightly low open circuit voltage (Voc) of similar to 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.