Easily Prepared Carbon Nanotubes Enabling Low Cost and Hole Transport Layer Free Perovskite Solar Cells.

Carbon electrodes (CEs) have emerged as promising electrodes for perovskite solar cells (PSCs) due to their effective hole extraction capability, excellent stability, and low cost, which are conducive to improving the device stability, simplifying the device structure, and reducing fabrication costs. However, their porous structure, limited conductivity, and interfacial energy level mismatch with perovskites lead to severe charge recombination. To address these issues, we designed β-cyclodextrin-grafted multiwalled carbon nanotubes (β-CD/MWCNTs) to modify a CE, in which β-CD can chelate Pb2+ ions and passivate defects by the hydroxyl groups and hydrophobic cavities, while MWCNTs enhance the conductivity of the CE. Notably, β-CD/MWCNTs act as a molecular bridge, converting the weak contact between the perovskite and CE into enhanced interfacial interaction, facilitating charge extraction and collection. The resulting CsPbBr3-based PSCs achieved a champion PCE of 10.48%. More importantly, the unencapsulated devices retained 84.6% of their initial efficiency after a 1000 h operation stability test in air, along with significantly reduced Pb leakage.