Record efficiency of 20.01% in HTM-free carbon-based CsPbI₃ perovskite solar cells achieved by TEPM multifunctional additive

(Figure presented.) All-inorganic, hole-transport-material-free (HTM-free), carbon-based perovskite solar cells (C-PSCs) have garnered significant attention due to their exceptional stability and low cost. However, their performance and commercial potential are still constrained by issues such as poor interfacial contact, insufficient crystallinity, and energy level misalignment. In this work, we tackle 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, thereby synergistically slowing crystallization kinetics to regulate crystal growth and passivate deep-level defects. As a result, the 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.