Simultaneously enhancing hole extraction and defect passivation with more conductive hole-selective self-assembled molecules for efficient inverted perovskite solar cells

Abstract

Suppressing the interfacial energy losses of the buried hole-selective layer (HSL) is essential to upgrade the power conversion efficiencies (PCEs) of inverted perovskite solar cells (PSCs). In this regard, innovations in hole-extraction materials featuring self-assembled molecule (SAM) characteristics show great potential. Herein, two SAMs of C-2PACz and S-2PACz based on phenyl- and thienyl-substituted carbazole units, respectively, were developed to serve as multifunctional HSLs. The pendant phenyl and thienyl units increase the dipole moment of the SAMs as compared to that of the standard control 2PACz, which was used to efficiently modulate the work function of ITO and form desirable energy level alignments with a perovskite absorber. C-2PACz and S-2PACz SAMs possess greater capability to passivate the interface defects of a perovskite absorber, especially S-2PACz, due to the electrostatic interaction between the under-coordinated Pb²⁺ and S of thiophene. C-2PACz and S-2PACz with increased conjugation also show higher conductivity to promote charge transport. Moreover, HSLs based on C-2PACz and S-2PACz form a template for the crystallization of the perovskite layer to achieve more dense and uniform crystalline grains and higher crystallinity. Owing to the above-mentioned synergistic effects, C-2PACz- and S-2PACz-derived solar cells exhibit low non-radiative recombination loss, higher PCEs and enhanced stability compared to the control device with 2PACz.