Perovskite solar cells (PSCs) have attracted significant attention as next-generation photovoltaic technologies due to their high power conversion efficiency, tunable bandgap properties, low-temperature fabrication processes, and compatibility with flexible photovoltaic applications.

In perovskite solar cells, hole transport materials (HTMs) play a critical role in extracting holes from the perovskite absorber layer and transporting them to the anode. The choice of HTM directly affects:

• Charge extraction efficiency

• Interfacial recombination losses

• Long-term device stability

• Manufacturing cost and scalability potential

J&K Scientific provides high-purity hole transport materials for photovoltaic research, covering organic small molecules, polymers, inorganic materials, and self-assembled monolayers (SAMs) to meet the needs of various device architectures and application scenarios.

What Are Hole Transport Materials?

Hole transport materials are functional layer materials used in perovskite solar cells to transport holes. In the device structure, the HTM layer is positioned between the perovskite absorber layer and the electrode, serving to selectively extract holes and block electrons.

An ideal HTM should satisfy the following criteria:

• Energy level alignment: The HOMO level should align with the valence band edge of the perovskite to reduce hole extraction barriers

• High hole mobility: Ensures rapid charge transport to the electrode, minimizing recombination losses

• Good film-forming properties: Forms uniform, pinhole-free films to prevent direct contact between the electrode and perovskite

• Chemical stability: Compatible with the perovskite layer, not triggering interfacial degradation reactions

• Cost-effectiveness: Simple synthesis route suitable for scalable production

Major Categories of Hole Transport Materials

HTMs used in perovskite solar cells can typically be classified into the following categories:

1. Organic small molecule HTMs

2. Polymeric HTMs

3. Inorganic HTMs

4. Self-assembled monolayers (SAMs)

5. Emerging HTM systems

Organic Small Molecule Hole Transport Materials

Spiro-OMeTAD CAS No.: 207739-72-8

Advantages:

• Good energy level alignment with lead halide perovskites, facilitating hole extraction

• Solution-processable, compatible with spin-coating techniques

• Has repeatedly achieved record efficiencies in n-i-p structured devices

Disadvantages:

• High cost, complex synthesis route, difficult purification

• Requires doping: Typically needs hygroscopic dopants such as Li-TFSI and tBP to enhance conductivity, but these dopants absorb moisture and accelerate device degradation

• Doping process requires exposure to atmospheric oxygen, increasing process complexity

Stability challenges: Dopants (especially Li⁺ ions) can migrate to the perovskite layer during long-term operation, inducing decomposition reactions and causing efficiency decay.

TCTA CAS No.: 139092-78-7

TCTA (4,4',4''-tris(carbazol-9-yl)triphenylamine) is a hole transport material commonly used in constructing high-efficiency perovskite solar cells.

Molecular formula: C₅₄H₃₆N₄

Characteristics:

• Contains carbazole groups with electron-rich, excellent thermochemical stability

• Solution-processable, suitable for various device architectures

Carbazole-Based Small Molecule HTMs

Carbazole-based HTMs have gained attention due to their electron-rich nature, low oxidation-reduction potential, and excellent thermochemical stability. J&K Scientific provides a variety of carbazole-based HTM materials, including 4PACz, MeO-4PACz, Br-4PACz, and others, suitable for different device architectures.

Polymeric Hole Transport Materials

PTAA CAS No.: 1333317-99-9

PTAA is a commonly used polymeric HTM in inverted (p-i-n) structures, known for its good thermal stability and film-forming properties.

Advantages:

• HOMO level well-matched with perovskite

• Can be used without doping, offering better stability than doped Spiro-OMeTAD

• Performs well in flexible devices and tandem cells

Disadvantages:

• Relatively low hole mobility, limiting its application in large-area devices

• Poor wettability with perovskite, requiring surface treatment (e.g., oxygen plasma, SAM layers, or NiOx interlayers) to improve interfacial contact

PEDOT:PSS CAS No.: 155090-83-8

PEDOT:PSS is one of the earliest polymeric HTMs applied in perovskite solar cells, commonly used in inverted structures.

Advantages:

• Solution-processable with mature technology

• High transparency, suitable for semi-transparent devices

Disadvantages:

• Intrinsic acidity (PSS component) may corrode electrodes and accelerate perovskite degradation

• High interfacial defect density, prone to non-radiative recombination

Inorganic Hole Transport Materials

Inorganic HTMs, their excellent chemical stability, high mobility, and low synthesis cost, are considered an important direction for promoting the commercialization of perovskite solar cells.

NiOₓ CAS No.: 1313-99-1

NiOₓ is the most extensively studied inorganic HTM, primarily used in inverted (p-i-n) structures.

Advantages:

• Excellent chemical and thermal stability

• Good energy level alignment with perovskite valence band

• Performance can be further optimized through Cu or Li doping

Disadvantages:

• High surface defect density, prone to inducing non-radiative recombination at the HTM/perovskite interface

• High-valence Niδ⁺ (δ ≥ 3) species may undergo redox reactions with perovskite components, accelerating degradation

CuSCN CAS No.: 1111-67-7

CuSCN is an efficient inorganic HTM with wide bandgap, high hole mobility, and simple synthesis.

Advantages:

• Hole mobility orders of magnitude higher than Spiro-OMeTAD

• Hydrophobic nature enhances device moisture stability

Disadvantages:

• Relatively low open-circuit voltage, requiring optimization through interface engineering

CuI CAS No.: 7681-65-4

CuI is another inorganic HTM that has attracted considerable attention, with performance comparable to CuSCN.

Advantages:

• High hole mobility

• Simple synthesis, low cost

• Hydrophobic properties beneficial for improving stability

Self-Assembled Monolayers (SAMs)

SAMs represent one of the most promising new directions in HTM research in recent years, signifying a paradigm shift from "bulk transport" to "interfacial engineering".

4PACz CAS No.: 20999-36-4

Ph-4PACz CAS No.: 2814500-04-2

MeO-4PACz CAS No.: 2922526-56-3

Br-4PACz CAS No.: 2996161-28-3

Core Advantages of SAMs:

• Highly ordered: Forms covalently bonded monolayers at the perovskite/electrode interface, achieving optimal interfacial contact

• Interfacial defect passivation: Significantly reduces interfacial recombination losses

• Dopant-free: Avoids stability issues caused by dopants

• Low-temperature, solution-processable: Compatible with roll-to-roll printing and other industrial-scale processes

Hole Transport Material Selection Guide