C-N linked donor type porphyrin derivatives: unrevealed hole-transporting materials for efficient hybrid perovskite solar cells

A new series of Zn(II) and Cu(II)-based porphyrin complexes 5a and 5b doubly functionalised with carbazole units were developed to be used as hole-transporting materials (HTMs) in perovskite solar cells (PSCs). These complexes were obtained via a nucleophilic substitution reaction mediated by PhI(OAc)2/ NaAuCl4 center dot 2H(2)O, or using C-N transition metal-assisted coupling. The hole extraction capability of 5a and 5b was assessed using cyclic voltammetry; this study confirmed the better alignment of the Zn(II) complex 5a with the perovskite valence band level, compared to the Cu(II) complex 5b. The optimised geometry and molecular orbitals of both complexes also corroborate the higher potential of 5a as a HTM. Photoluminescence characterisation showed that the presence of 5a and 5b as HTMs on the perovskite surface resulted in the quenching of the emission, matching the hole transfer phenomenon. The photovoltaic performance was evaluated and compared with those of reference cells made with the standard HTM spiro-OMeTAD. The optimised 5-based devices showed improvements in all photovoltaic characteristics; their open circuit voltage (Voc) reached close to 1 V and short-circuit current density ( Jsc) values were 13.79 and 9.14 mA cm(-2) for 5a and 5b, respectively, disclosing the effect of the metallic centre. A maximum power conversion efficiency (PCE) of 10.01% was attained for 5a, which is 65% of the PCE generated by using the spiro-OMeTAD reference. This study demonstrates that C-N linked donor-type porphyrin derivatives are promising novel HTMs for developing efficient and reproducible PSCs.

Automated summary

A new series of Zn(II) and Cu(II)-based porphyrin complexes 5a and 5b, functionalised with carbazole units, were developed as hole-transporting materials (HTMs) in perovskite solar cells (PSCs). These complexes were obtained via nucleophilic substitution reaction or using C-N transition metal-assisted coupling. The study confirmed that Zn(II) complex 5a had better alignment with the perovskite valence band level and higher potential as an HTM compared to Cu(II) complex 5b. The photovoltaic performance of the optimized complexes showed improved characteristics, with a maximum power conversion efficiency (PCE) of 10.01% for 5a. These C-N linked porphyrin derivatives demonstrate promise as novel HTMs for efficient and reproducible PSCs.