Dopant-free tert-butyl Zn(ii) phthalocyanines: the impact of substitution on their photophysical properties and their role in perovskite solar cells

Abstract

We synthesized molecular hole-transporting materials (HTMs) featuring a zinc phthalocyanine (ZnPc) central core and modulated the non-peripheral position with different numbers of tert-butyl groups. The synthesized molecules were then integrated into the fabrication of perovskite solar cells to evaluate their efficacy. We studied four different undoped ZnPcs with four (ZnPc 1), three (ZnPc 2), two (ZnPc 3), and one (ZnPc 4) tert-butyl group as hole transport materials in the n–i–p configuration. Among them, ZnPc 1 registered the best power conversion efficiency of 15.50%, an open-circuit voltage (V_oc) of 932.9 mV, a short-circuit current density (J_sc) of 24.26 mA cm⁻², and a fill factor (FF) of 68.46%. This was followed by ZnPc 2 which achieved a modest 7.98% performance. The surface microstructure is greatly influenced by the type of molecule and it evolves from a compact granular to a fibrillar structure. Furthermore, the devices with ZnPc 1 showed enhanced stability under an ambient atmosphere comparable to Spiro-OMeTAD.