Research Paper: Small Molecular Organic Hole Transport Layer for Efficient Inverted Perovskite Solar Cells

Summary

This study addresses the need for cost-effective, dopant-free, and low-temperature processable hole transport layers (HTLs) for commercial inverted perovskite solar cells (PSCs). The main goal was to introduce and evaluate a small molecular material, 4,4′,4″-Tris[2-naphthyl(phenyl)amino]triphenylamine (2TNATA), as an HTL for the first time. Key findings demonstrate that 2TNATA exhibits excellent thermal stability and offers proper energy alignment with the perovskite valence band. Perovskite films deposited on 2TNATA showed superior crystallinity and morphology with fewer defects compared to those on conventional PEDOT:PSS and PTAA. Furthermore, 2TNATA-based PSCs displayed superior carrier kinetics, including faster carrier transfer, higher built-in potential, and reduced recombination. Consequently, 2TNATA HTL-based PSCs achieved an outstanding power conversion efficiency (PCE) of 20.58% for 0.09 cm² devices, outperforming PTAA (19.36%) and PEDOT:PSS (14.35%). An impressive PCE of 20.04% was also observed for larger 1.0 cm² devices, along with good reproducibility and storage stability.

Why it matters

These findings are crucial for overcoming the cost and stability limitations of existing HTLs in PSCs, which hinder their commercialisation. 2TNATA provides a dopant-free, significantly cheaper (over ten times less expensive than PTAA), and low-temperature processable alternative. This advances the development of more durable, efficient, and economically viable PSCs, making them suitable for large-area fabrication and potentially flexible applications, thereby accelerating the widespread adoption of next-generation solar energy technologies.

How Fluxim tools used

The PAIOS system from Fluxim AG was instrumental in investigating the carrier kinetics of the PSCs. Specifically, it was used for electrochemical impedance spectroscopy (EIS), which confirmed higher recombination resistance in 2TNATA-based devices, indicating reduced interface recombination and enhanced carrier transport efficiency. Transient photovoltage (TPV) decay analysis was also conducted using PAIOS, demonstrating longer photovoltage decay times for 2TNATA HTL-based PSCs, which signifies higher carrier lifetime and lower interface recombination velocity. These precise measurements helped to validate the superior charge transport and reduced losses in devices using 2TNATA.

Publication Details

Ahmmed, S., Karim, M. A., He, Y., Cao, S., Kayesh, M. E., Matsuishi, K., & Islam, A. (2025). Small Molecular Organic Hole Transport Layer for Efficient Inverted Perovskite Solar Cells. Solar RRL, 7, e202500017. https://doi.org/10.1002/solr.202500017