New strategy stabilizes the perovskite/C60 interface, delivering 27.43% efficiency

Source Summary

Researchers from China's Northwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene (NPU) and Southern University of Science and Technology have developed a new interfacial strategy that addresses a stubborn weak point in inverted perovskite solar cells (PSCs): the instability of the fullerene (C60) electron transport layer. C60 and its derivatives are popular choices for electron transport layers in inverted PSCs thanks to their high electron mobility and favorable energy-level alignment with the perovskite, but suffer from intrinsic drawbacks. Its electronic disorder promotes trap-assisted recombination, which narrows the quasi-Fermi level splitting and drags down the open-circuit voltage. Just as importantly, C60's high molecular symmetry and weak intermolecular bonding make it prone to thermodynamically driven aggregation as the film forms - which worsens under light and heat. As the fullerene agglomerates, contact across the perovskite/C60 interface deteriorates, interface resistance climbs, charge transport suffers, and the device degrades faster. Functionalized C60 derivatives can improve compatibility and morphology, but the added groups often leave the material even more vulnerable to stress-induced breakdown. To break this cycle, the team designed an acceptor-donor-type metallopolymer, "polycarbolong," and used it to build what they call a corrugated polycarbolong interlocking (CPI) layer at the interface.