Hole Transport Materials in Perovskite Solar Cell Technologies

Hybrid organic–inorganic perovskite solar cells have emerged as a leading photovoltaic technology, achieving power conversion efficiencies exceeding 25 per cent with low-cost solution processing. Central to this performance are hole transport materials (HTMs), which extract and convey positive charge carriers from the perovskite absorber to the electrode. The ideal HTM must combine suitable energy-level alignment, high hole mobility and robust environmental stability. Small-molecule compounds such as spiro-OMeTAD and polymeric materials like PTAA have dominated early developments, but both require hygroscopic dopants to achieve sufficient conductivity, which can promote ion migration and accelerate device degradation. Recent efforts focus on alternative organic architectures incorporating heterocyclic backbones, self-assembled monolayers and crystalline frameworks, as well as advances in interfacial engineering—gelation, multilayer doping profiles and hydrophobic additives—to produce pinhole-free films with suppressed defect formation. By balancing electrical performance with enhanced moisture and thermal resilience, these strategies pave the way for commercialisation of perovskite photovoltaics in flexible substrates, tandem configurations and large-area modules.

Research from Nature Portfolio

Recent studies have elucidated the mechanisms by which mobile ions, notably iodide and organic cations, migrate from the perovskite into the adjacent hole transport layer at elevated temperatures, disrupting dopant oxidation and degrading conductivity. By tailoring interface chemistry and adopting passivating interlayers, researchers have demonstrated reduced ion diffusion and sustained electrical properties under thermal stress. In parallel, the implementation of vacuum-deposited, triple-layer HTM architectures with optimised n-i-p doping profiles has yielded pinhole-free films that maintain high open-circuit voltages and stable power outputs over hundreds of hours of air exposure, underscoring the importance of precise dopant distribution and interfacial design for long-term device resilience.

Hole Transport Materials in Perovskite Solar Cell Technologies publication trend

The graph below shows the total number of articles in hole transport materials in perovskite solar cell technologies across all publications each year (not limited to Nature Index journals).

Technical terms

Hole transport material (HTM): A semiconducting layer that selectively extracts positive charge carriers (holes) from the perovskite absorber to the back electrode.

Spiro-OMeTAD: A benchmark small-molecule HTM based on a spirobifluorene core, widely used in perovskite solar cells and typically doped to enhance conductivity.

n-i-p architecture: A device configuration comprising an electron-transport layer (n), the intrinsic perovskite semiconductor (i) and a hole transport layer (p), often achieved by sequential deposition.

Ion migration: The movement of ionic species (e.g. halide anions, organic cations) within the perovskite or across interfaces, which can undermine electrical performance and operational stability.

Inverted device: A perovskite solar cell structure in which the hole transport layer is deposited first on the transparent electrode, followed by the perovskite and then the electron transport layer, offering advantages in stability and fabrication simplicity.

References

1. Gelation of Hole Transport Layer to Improve the Stability of Perovskite Solar Cells. Nano-Micro Letters (2023).
2. Relationship between ion migration and interfacial degradation of CH3NH3PbI3 perovskite solar cells under thermal conditions. Scientific Reports (2017).
3. Pinhole-free hole transport layers significantly improve the stability of MAPbI 3 -based perovskite solar cells under operating conditions. Journal of Materials Chemistry A (2015).
4. Lessons learned from spiro-OMeTAD and PTAA in perovskite solar cells. Energy & Environmental Science (2021).
5. Molecular materials as interfacial layers and additives in perovskite solar cells. Chemical Society Reviews (2020).
6. Opportunities and challenges of hole transport materials for high‐performance inverted hybrid‐perovskite solar cells. Exploration (2023).
7. Heterocyclic and heteropolycyclic moieties in organic hole transport materials for perovskite solar cells: Design, synthesis, and performance. Coordination Chemistry Reviews (2025).
8. A Generic Route of Hydrophobic Doping in Hole Transporting Material to Increase Longevity of Perovskite Solar Cells. Joule (2018).