Record Efficiency of 20.01% in HTM-Free Carbon-Based CsPbI3 Perovskite Solar Cells Achieved by TEPM Multifunctional Additive
All-inorganic, hole-transport-material-free (HTM-free), carbon-based perovskite solar cells (C-PSCs) have attracted significant attention due to their exceptional stability and low cost. However, their performance and commercial potential are constrained by poor interfacial contact, insufficient crystallinity, and energy level misalignment. In this work, we address these challenges via a molecular engineering strategy by introducing tetrakis(4-ethynylphenyl)methane (TEPM) as a multifunctional additive. The alkynyl moiety (C≡C) in TEPM coordinates with Pb2+ ions in perovskite precursors, synergistically slowing crystallization kinetics to regulate crystal growth and passivate deep-level defects. Consequently, CsPbI3 films exhibit larger grain sizes, improved crystallinity, and lower defect densities. Devices modified with TEPM achieved a record power conversion efficiency (PCE) of 20.01% (certified 19.58%). Additionally, unencapsulated devices retained 87.6% of their initial efficiency after 1080 h under ambient conditions (25 °C, 30% relative humidity), and maintained 94.0% of their initial efficiency after 730 h of continuous AM 1.5G illumination in air. This work sets a new efficiency benchmark for inorganic HTM-free C-PSCs and provides a versatile molecular engineering strategy for developing high-performance, stable perovskite photovoltaics.