# Chemical Compatibility of n-Type Dopants for SWCNT Cathodes in Inverted Perovskite Solar Cells

## TL;DR

Researchers tested different n-type dopants for carbon nanotube cathodes in solar cells, finding that chemical compatibility is key to efficient and stable performance.

## Contribution

The study identifies polymeric and coordination-type dopants as chemically compatible with perovskites, enabling efficient and stable n-type SWCNT cathodes.

## Key findings

- Polymeric and coordination-type dopants preserve perovskite crystallinity and surface uniformity.
- PEI- and TPP-doped SWCNT electrodes achieved power conversion efficiencies of 9.6% and 8.1%.
- Interfacial chemical compatibility, not intrinsic donor strength, determines doping effectiveness.

## Abstract

The advancement of efficient and stable perovskite solar cells (PSCs) increasingly depends on developing flexible, metal-free electrode architectures. Single-walled carbon nanotubes (SWCNTs) offer chemical robustness, high conductivity, and mechanical flexibility, making them promising candidates to replace brittle metal cathodes. However, pristine SWCNTs are intrinsically p-type, creating energy barriers and recombination losses in inverted (p–i–n) PSCs. Achieving stable n-type doping compatible with both SWCNTs and perovskites is therefore critical. Here, seven representative n-type dopants, small molecules (TBD and TPP), ionic salts (TBAI, TBABr, and B18C6·KCl), and polymers (PEI and PVP) were systematically investigated to elucidate their effects on doping efficiency and interfacial stability. Morphological, structural, and electronic analyses supported by DFT calculations reveal that strong bases and ionic dopants promote perovskite degradation, whereas polymeric and coordination-type dopants preserve crystallinity and surface uniformity. Among them, PEI- and TPP-doped SWCNT electrodes achieved the best device performance, with power conversion efficiencies of 9.6% and 8.1%, respectively, demonstrating efficient electron extraction and interfacial stability. These findings highlight that interfacial chemical compatibility rather than intrinsic donor strength governs the effectiveness of n-type SWCNT doping, providing rational design principles for stable, metal-free perovskite photovoltaics.