Coordination-based doping of MEH-PPV with La(TFSI)3 enables air-free conductivity and stable performance in perovskite solar cells

Abstract

Achieving high electrical conductivity in conjugated polymers without negatively impacting morphology and stability remains a central challenge in the development of organic optoelectronic devices. Here, we demonstrate that doping MEH-PPV with lanthanum bistriflimide [La(TFSI)3] results in a conductivity enhancement exceeding six orders of magnitude under fully inert conditions. Unlike monovalent dopants such as LiTFSI, which require environmental activation and lead to morphological defects, La(TFSI)3 enables oxygen-independent conductivity by forming multidentate coordination complexes with polymer sidechains. Spectroscopic analyses (FTIR, Raman, PL) indicate that La3+ induces crosslinking and suppresses emissive disorder, promoting interchain charge hopping even without generating polarons. Morphological studies show that La3+ doping eliminates pinholes and produces structurally cohesive films, in contrast to the inhomogeneous and unstable films produced with LiTFSI. When used as a hole transport layer in perovskite solar cells, La(TFSI)3 doped MEH-PPV increases the power conversion efficiency from 13.05 % to 18.50 % and enables devices that retain 100 % of their efficiency after 1000 h of inert storage. These results highlight a coordination-driven, air-free doping strategy for enabling durable, high-performance organic electronics.