Dopant-Free Hole Transport Materials in Perovskite Solar Cells

Perovskite solar cells (PSCs) have emerged as a leading photovoltaic technology owing to their high power conversion efficiencies and potential for low-cost fabrication. A key component in these devices is the hole transport material (HTM), which extracts and shuttles positive charges (holes) from the perovskite absorber to the electrode. Traditional HTMs rely on chemical dopants to enhance conductivity, but these additives often compromise long-term stability by attracting moisture or inducing ion migration. Recent efforts have therefore focused on designing dopant-free HTMs that combine intrinsic high mobility with robust environmental tolerance. Molecular engineering strategies include the introduction of rigid π-conjugated backbones to promote close packing, donor–acceptor architectures to control energy levels and solubility, and surface-passivating units to reduce trap density at the perovskite interface. Both small molecules and conjugated polymers have demonstrated promising performance when processed under air or low-temperature conditions, offering routes to scalable and stable PSC modules. Progress in this area addresses one of the principal barriers to commercial deployment of perovskite photovoltaics by delivering efficient charge transport without the drawbacks of conventional salt dopants.

Research from Nature Portfolio

Recent studies have shown that certain conjugated polymers can function effectively as undoped HTMs when carefully processed. In one foundational work, researchers replaced conventional doped spiro-OMeTAD layers with non-doped MEH-PPV and P3HT materials via one- and two-step solution methods. Optimisation of polymer concentration and solvent choice led to hysteresis-free performance, demonstrating that MEH-PPV can achieve respectable power conversion efficiencies in the absence of dopants. While the champion cells remained below those using salt-doped spiro-OMeTAD, this effort established key processing parameters and morphological controls that inform the design of future dopant-free polymer HTMs.

Dopant-Free Hole Transport Materials in Perovskite Solar Cells publication trend

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

Technical terms

Perovskite: A crystal structure typified by the formula ABX₃, here referring to metal-halide semiconductors used in solar absorbers.

Hole Transport Material (HTM): A layer in a solar cell that selectively extracts and transports positive charge carriers (holes) to the electrode.

Dopant-Free: A material design that does not require added ionic or molecular dopants to achieve high electrical conductivity.

Power Conversion Efficiency (PCE): The fraction of incident solar energy converted into electrical power by a photovoltaic device.

π–π Stacking: Attractive interactions between aromatic rings that facilitate charge transport through ordered molecular packing.

References

1. Efficiency Enhancement of Hybrid Perovskite Solar Cells with MEH-PPV Hole-Transporting Layers. Scientific Reports (2016).
2. Fluorine substitutions engineering of benzotriazole‐based hole transport polymers toward high‐performance CsPbI2Br perovskite solar cells. Battery Energy (2024).
3. Dopant-Free Hole-Transporting Material Based on Poly(2,7-(9,9-bis(N,N-di-p-methoxylphenylamine)-4-phenyl))-fluorene for High-Performance Air-Processed Inverted Perovskite Solar Cells. Polymers (2023).
4. Conformational and Compositional Tuning of Phenanthrocarbazole-Based Dopant-Free Hole-Transport Polymers Boosting the Performance of Perovskite Solar Cells. Journal of the American Chemical Society (2020).