Innovating Carbon-based Perovskite Solar Cells: the Role of a Cn-anchoring Self-assembled Molecular Layer in Efficiency and Stability

The discovery of self-assembled molecular layers (SAMLs) containing anchoring groups such as COOH and PO3H as efficient hole-selective materials (HSMs) in p-i-n perovskite solar cells (PSCs) is pivotal to enhancing the interaction between HSMs and perovskite layers. In this work, we propose, for the first time, an HSM featuring CN groups as anchoring groups in n-i-p devices, achieving a maxmium power conversion efficiency (PCE) of 20.37% (mean value = 19.83%) using a carbon electrode. The HSM is based on a phenanthroimidazole backbone linked to aza and cyanide groups. VASP computational studies reveal that the new HSM can coordinate to Pb atoms in the perovskite layer through CN groups in a bridging mode (where two CN groups bond to two Pb atoms), with an adsorption energy (Eads) of -1.04 eV. These SAMLs demonstrate greater stability compared to the classic spiro-OMeTAD, with a remarkable one-year operational stability. The photostability and thermal stability of PSCs incorporating the new SAMLs are notable, retaining approximately 97.5% of their initial PCE after 600 hours at 80 degrees C under ambient conditions. Additionally, the devices have exhibited impressive visual stability for over one year. The operational stability of PSCs based on carbon electrodes, combined with the versatility of CN-functionalized organic molecules, positions these materials as promising candidates for the large-scale production of PSCs with metal-free electrodes, eliminating the need for thermal evaporation techniques. Our findings represent a paradigm shift from conventional spiro-OMeTAD-based hole transporting materials to novel SAML-based HSMs, paving the way for advancements in PSC technology.