Interface engineering via pre-engineered black phosphorus quantum dots for highly efficient carbon-based hole-transport-layer-free perovskite solar cells

Abstract

Carbon-electrode-based perovskite solar cells (C-PSCs) without a hole transport layer (HTL) have attracted considerable attention due to their simple fabrication, low cost, and easy scalability. However, inefficient physical and electrical contact at the perovskite/carbon interface remains a major challenge, impairing hole extraction and promoting charge recombination. In this study, we introduce a pre-engineered and multifunctional interlayer for planar HTL-free C-PSCs based on tetrabutylammonium ion (TBA + )-intercalated black phosphorus quantum dots (BPQDs). These BPQDs are synthesized via an electrochemical intercalation-assisted liquid-phase ultrasonic exfoliation method using a TBACl-containing electrolyte. The TBA + modification endows the BPQDs with their final desired properties preengineered, with enhanced conductivity and raised valence band maximum (-5.27 eV). This creates a favorable cascade energy-level alignment between the perovskite absorber (-5.5 eV) and the carbon electrode (-5.0 eV), thereby facilitating hole extraction. The insertion of this fine BPQDs interlayer also results in seamless contact at the perovskite/carbon interface, promoting interfacial charge transfer. Furthermore, the active TBA + ions and Cl -released from BPQDs-TABCl also effectively passivate defects on the perovskite surface and thus suppress nonradiative recombination. Consequently, the planar HTL-free C-PSCs achieve a notable increase in power conversion efficiency (PCE) from 13.76% to 17.08%, along with excellent operational stability.