Simultaneous ambient long-term conductivity promotion, interfacial modification, ion migration inhibition and anti-deliquescence by MWCNT:NiO in spiro-OMeTAD for perovskite solar cells

Abstract

The lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI)-doped spiro-OMeTAD hole transport layer (HTL) suffers from poor ambient long-term conductivity, detrimental ion migration, and inability to passivate perovskite defects at the perovskite/HTL interface, which seriously hinders obtaining efficient and stable perovskite solar cells (PSCs). Here, to address all these issues, a multifunctional NiO quantum dot (QD)-modified multi-walled carbon nanotube (MWCNT:NiO) additive is added to spiro-OMeTAD. By virtue of the high conductivity, hydrophobicity and anchoring effect of MWCNT:NiO on Li-TFSI through Li-O chemical bonds, the ambient long-term conductivity, restricting Li⁺ ion migration and anti-deliquescence of the doped HTL are effectively improved. Meanwhile, better energetic alignment, reduced interfacial defects and the loss of organic FA⁺/MA⁺ cations at the perovskite/HTL interface are achieved due to the added MWCNT:NiO. Consequently, the optimized MWCNT:NiO-based PSC exhibits an impressive PCE (22.73%) as well as a pronounced stability for over 1200 h under ambient conditions without encapsulation (room temperature, 30–50% relative humidity). These results demonstrate that the incorporation of such a multifunctional MWCNT:NiO material provides a promising strategy to combine interface engineering and HTL optimization, which is conductive to the realization of efficient and stable PSCs as well as other perovskite-based electronics.