Publication date: 5th November 2025
Self-assembled monolayers (SAMs) have attracted significant interest as hole transport layers (HTLs) for inverted perovskite solar cells (i-PSCs), as they have the advantages of high coverage on rough substates, optical loss, and easy adjustment of energy levels.[1] Not only electrical properties can be manipulated, but the molecular engineering design of SAM also enables adjustment of the interface between perovskite and HTLs. Carbazole-typed SAMs such as [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) have led to great success in the realization of high-efficiency i-PSCs.[2] Although various carbazole-typed SAMs have been reported so far, there have been few reports comparing their performance based on differences in the alkyl spacer length. Here in, we synthesized carbazole-typed SAMs (T-PACz, T-2PACz, T-3PACz, T-4PACz), which have the alkyl spacer of different lengths. Furthermore, they have thienyl-substituted carbazole unit, which are known to possess greater capability to passivate the interface defects of a perovskite absorber.[3, 4] We fabricated i-PSCs using these SAMs as a HTL and compared the effect of this alkyl spacer length on the device performance as SAMs. As a result, the PSCs based on T-4PACz which has butylene spacers showed highest PCE among them (Figure 1). The reason for this result is thought to be that T-4PACz has the highest solubility in organic solvents due to butylene spacers and exhibits excellent film-forming properties for SAMs. Moreover, the PSCs based on T-4PACz showed improved performance and enhanced thermal stability compared to the PSCs based on 2PACz. These results obtained here are expected to be highly useful for optimizing SAM properties as HTL of PSCs and studying for novel molecular design in the future.
This study was supported by the Project JPNP21016, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).
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