(Invited) Modification of Perovskite Layer for Efficient Perovskite Solar Cells
Authors: Wakamiya Atsushi 
Published: December 2024

Perovskite solar cells are expected as promissing photovoltaics, offering a path to highly efficient solar energy conversion.1–4 Surface modification of perovskite layer is crucial to improve device performance and durability. In this talk, our recent progress on the development of charge collecting materials and surface modification with dipole strategy will be shown.

Optimized Carrier Extraction at Interfaces
4-7

Carrier extraction in mixed tin–lead perovskite solar cells is improved by modifying the top and bottom perovskite surfaces with ethylenediammonium diiodide and glycine hydrochloride, respectively. Trap densities in the perovskite layers are reduced as a result of surface passivation effects and an increase in film crystallinity. In addition, the orientated aggregation of the ethylenediammonium and glycinium cations at the charge collection interfaces result in the formation of surface dipoles, which facilitate charge extraction. As a result, the treated mixed tin–lead perovskite solar cells showed improved performance, with a fill factor of 0.82 and a power conversion efficiency up to 23.6%.5 The unencapsulated device also shows improved stability under AM1.5G, retaining over 80% of the initial efficiency after 200 h continuous operation in inert atmosphere. Our strategy is also successfully applied to centimeter-scale devices, with efficiencies up to 21.0%.

Tripodal Hole-Collecting Monolayer Materials
8

Hole-collecting monolayers have drawn attention in perovskite solar cell research due to their ease of processing, high performance, and good durability. Since molecules in the hole-collecting monolayer are typically composed of functionalized π-conjugated structures, hole extraction is expected to be more efficient when the π-cores are oriented face-on with respect to the adjacent surfaces. However, strategies for reliably controlling the molecular orientation in monolayers remain elusive. In this work, multiple phosphonic acid anchoring groups were used to control the molecular orientation of a series of triazatruxene derivatives chemisorbed on a transparent conducting oxide electrode surface. Using infrared reflection absorption spectroscopy and metastable atom electron spectroscopy, we found that multipodal derivatives align face-on to the electrode surface, while the monopodal counterpart adopts a more tilted configuration.8 The face-on orientation was found to facilitate hole extraction, leading to inverted perovskite solar cells with enhanced stability and high-power conversion efficiencies up to 25.0%.

Acknowledgements

:
This work was partially supported by
the JST-Mirai Program (JPMJMI22E2),
NEDO (
JPNP21016),
, the International Collaborative Research Program of ICR, Kyoto University, etc.

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