Singlet diradicaloids as n-type passivating interlayers for CsPbI3 perovskite solar cells

Abstract

The interface modification of halide perovskite materials is a fundamental step to obtain efficient charge extraction, passivation of defects and improved stability of polycrystalline active layers at the core of perovskite-based solar cells. For CsPbI₃ inorganic perovskite, this is particularly critical due to the usual formation of surface defects during perovskite crystallization, leading to increased nonradiative recombination and energy mismatch with organic transporting layers. Here we propose the use of a polychlorinated thiele hydrocarbon (TTH), i.e. a stable singlet diradicaloid belonging to the family of para-quinodimethanes, that uniquely combines the dynamic generation of a charge transfer zwitterionic excited state with excellent photostability. We proved that the use of the TTH molecule as a CsPbI₃ interface modifier in inverted photovoltaic devices significantly enhances the open circuit voltage of the device. This is due to a convenient synergy between efficient Pb passivation from the chlorine substituents, optimal energy level alignment and the light-triggered dipole that, overall, reduces the resistance to the charge transfer. This work paves the way to the employment of singlet diradicaloids in perovskite solar cells.