High performance inverted planar perovskite solar cells enhanced by heteroatomic functionalized hole transport materials†

Two organic small molecule hole transport materials, 5-((3,6-bis(4-(bis(4-methoxyphenyl)amino)phenyl)thieno[3,2-b]thiophen-2-yl)methylene)-3-ethyl-2-thioxothiazolidin-4-one (shortly named C3-D) and 5,5′-((3,6-bis(4-(bis(4-methoxyphenyl)amino)phenyl)thieno[3,2-b]thiophene-2,5-diyl)bis(methaneylylidene))bis(3-ethyl-2-thioxothiazolidin-4-one) (shortly named C3-S), are designed with rhodanine as the functional group and utilized in inverted planar perovskite solar cells (PSCs). With the functional group, both HTMs exhibit good mobility, matching HOMO/LUMO energy levels and excellent interactions with ITO and the perovskite layer, enhancing hole extraction, transport, and defect passivation in inverted PSCs. As a result, the device based-on C3-D presents a champion power conversion efficiency (PCE) of 21.50% with J_SC = 24.49 mA cm⁻², V_OC = 1.072 V, and FF = 81.9%, while the device based-on C3-S shows a PCE of 19.24% with J_SC = 23.11 mA cm⁻², V_OC = 1.065 V, and FF = 78.2%. Additionally, the C3-D-based device also demonstrates superior stability compared to C3-S, retaining over 85% of the initial value after being kept for 500 h at room temperature in ambient air at 35% relative humidity, and over 60% of the initial value after being kept for 500 h at 85 °C in a N₂ glovebox, respectively. These results far surpass the performance of devices based-on a non-functional HTM, TT-3,6-TPA, as reported in the literature (a PCE of 0.7% with J_SC = 2.90 mA cm⁻², V_OC = 0.95 V, and FF = 27.0%). Therefore, these findings indicate that combining hetero-atomic functionalized groups with typical hole transport fragments could be a promising research avenue for enhancing the performance of inverted planar PSCs and facilitating the commercialization of perovskite solar cells.