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Self-Assembled Monolayers Explained | Perovskite Solar Cells

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TECHNOLOGY EXPLAINER

Self-Assembled Monolayers (SAMs)
— a hole exit made from a single layer of molecules

A SAM lines up a single layer of molecules on the surface of a transparent electrode to serve as the exit for holes. Molecules such as 2PACz, MeO-2PACz and Me-4PACz have underpinned records for inverted (p-i-n) perovskite solar cells and for perovskite-silicon tandems. The idea behind them is close to something materials engineers know well: a surface treatment agent.

Built from primary sources: peer-reviewed papers (Science, Nature Materials, Advanced Energy Materials, Energy & Environmental Science, ACS Applied Materials & Interfaces, Nature Communications) / Last updated September 2026

Conceptual image of a single round, clear droplet sitting on a smooth plain glass surface against a dark background, soft light reflected on it
AI-generated concept image. An impression of the idea that a layer of molecules too thin to see can change the character of a surface. It does not represent a real contact angle, material or measurement.
What this article covers
  1. What a SAM is, in three points
  2. The three parts of the molecule — anchor, linker, head
  3. How to read the 2PACz family
  4. Milestones — from the first report in 2018 to certified efficiencies above 27%
  5. A materials engineer's view (1): SAMs are cousins of coupling agents
  6. Weakness 1: incomplete coverage and clumping
  7. Weakness 2: acid attacks the layer below; heat and UV break the molecule
  8. A materials engineer's view (2): designing the acidity of the anchoring group
  9. Our calculation: how many molecules does 1 m² take?
  10. Strengths and open problems
  11. Glossary / References / Claim-to-source audit
How claims are labelled in this article

Sourced = stated in published material (link given)
Our calculation = a value this article derived from assumptions it states
Not yet confirmed = a plan, target or outlook with no confirmed track record
Structural readings and materials-design interpretations are marked separately as Commentary. Every efficiency figure is given with whether it is certified, and its area.

1. What a SAM is, in three points

A self-assembled monolayer (SAM) is a film one molecule thick, formed when molecules spontaneously bond to and line up on a substrate surface. In perovskite solar cells, it is formed on the transparent electrode (ITO or similar) and used as the layer that extracts holes.

  • The first report: in 2018 Magomedov et al. first used a SAM as a dopant-free hole-selective contact in a p-i-n cell, reaching 17.8% efficiency and an average fill factor of close to 80%, with parasitic absorption too small to detectSourced
  • How it is made: in the same paper, the substrate was simply dipped in a solution of a new molecule (V1036), which bonded to the ITO surface through a phosphonic acid anchoring groupSourced
  • Why it caught on: a 2025 Nature Communications paper (Qu et al.) lists the advantages of SAMs as tunable energy levels, low synthesis cost, low parasitic absorption, and the ability to passivate defects in both the perovskite above and the transparent electrode belowSourced
The single most important line in this article

A SAM's performance is set not only by the molecule's head but by its foot, the anchoring group. Papers from 2025 and 2026 reported in quick succession that phosphonic acid anchoring groups act as acids and corrode the NiOx underneathSourced, and that heat makes them form anhydrides and break downSourced. The chemistry of the functional group that bonds to the substrate is the territory of surface-treatment engineers.

2. The three parts of the molecule — anchor, linker, head

Qu et al. describe their SAM molecules in three parts: the head, the linker and the anchoring groupSourced. Many SAM molecules can be read in terms of this three-part structure.

The three parts of a SAM molecule, and where it sits in the cell (concept) Molecules drawn schematically as sticks; not chemical structure, size or density (schematic by this article) Perovskite (absorber) Transparent electrode (e.g. ITO) / NiOx Glass substrate Head: carbazole or similar Touches the perovskite and takes up holes Linker: alkyl chain or similar Joins head to anchor; length changes properties Anchoring group: phosphonic acid etc. Bonds to the surface of the oxide below Note: the three-part naming follows Qu et al. [Ref. 8]; bonding to ITO via phosphonic acid follows Magomedov et al. [Ref. 1]. Note: SAMs formed on NiOx follow the examples of Phung et al. [Ref. 4] and Chen et al. [Ref. 10]. Note: number, spacing, tilt and length of the molecules are schematic; they do not show real packing density or orientation.
Fig. 1 Concept diagram (vector drawing). Dividing the molecule into head, linker and anchoring group follows Qu et al. [Ref. 8]; the anchoring group bonding to ITO follows Magomedov et al. [Ref. 1]; SAMs on NiOx follow Phung et al. [Ref. 4] and Chen et al. [Ref. 10]. The shape, number, length and orientation of the molecules are all schematic and do not show chemical structure or real packing density.

The perspective by Hooijer et al. (EES, 2026) explains that SAMs formed on a transparent conductive oxide make covalent or ionic bonds and become stable, densely packed interfacial layers. Phosphonic acid groups are fixed by strong bidentate and tridentate bonds, while silane-based SAMs can gain long-term stability through Si–O–Si cross-linking at the cost of a higher risk of hydrolysisSourced.

3. How to read the 2PACz family

Once you know the chemical names, the names of the SAM molecules widely used in perovskite solar cells tell you their structure.

Short nameChemical name (as given in the paper)HeadLinkerAnchoring group
2PACz(2-(9H-carbazol-9-yl))ethylphosphonic acidCarbazoleEthyl (two carbons)Phosphonic acid
MeO-2PACz[2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acidCarbazole with two methoxy groupsEthyl (two carbons)Phosphonic acid
Me-4PACz(4-(3,6-dimethyl-9H-carbazole-9-yl)butyl)phosphonic acidCarbazole with two methyl groupsButyl (four carbons)Phosphonic acid

Chemical names are Sourced (2PACz: Du et al. [Ref. 12]; MeO-2PACz: Phung et al. [Ref. 4]; Me-4PACz: Chen et al. [Ref. 10]). The breakdown into head, linker and anchoring group is this article's own, based on the chemical names.

In 2019 a group including HZB published a paper in EES using monolayer hole-selective contacts in both single-junction and monolithic tandem cellsSourced. The naming works like this: “PA” is phosphonic acid, “Cz” is carbazole, the number is the number of carbons in the linker, and “MeO-” or “Me-” is the substituent on the head (this article's reading of the chemical names). The silicon tandem with a certified efficiency of 29.15% reported in Science in 2020 by a group including HZB used a methyl-substituted carbazole SAM as its hole-selective layer, speeding up hole extraction and reducing non-radiative recombination at the interfaceSourced.

4. Milestones — from the first report in 2018 to certified efficiencies above 27%

Milestones for cells using SAMs (this article's framing) Values as reported in each paper. Certification status and area in the lower rows 2018 2020 2024 2025 2026 17.8% 29.15% 24.68% 26.39% 27.1% First SAM hole layer formed by dipping Si tandem methyl carbazole SAM 2PACz aggregation curbed by co-adsorbate π-extended head ordered bilayer Redesigned to resist UV light and heat Paper's value Certified Certified Certified Certified Single junction Tandem Single junction Single junction 0.0715 cm² Single junction Note: Magomedov et al. 2018 [Ref. 1], Al-Ashouri et al. 2020 [Ref. 3], Li et al. 2024 [Ref. 11], Qu et al. 2025 [Ref. 8], Zhan et al. 2026 [Ref. 7]. Where no area is shown, none is given in the abstract this article checked. Note: single-junction and tandem cells, areas and test centres differ, so efficiencies cannot be compared directly. Note: the choice of five milestones is this article's own; this is not a comprehensive timeline.
Fig. 2 Concept diagram (vector drawing). The efficiency and content at each point follow the abstracts of the respective papers [Refs. 1, 3, 7, 8 and 11]. The choice of milestones is this article's own; this is not a comprehensive timeline. Single-junction versus tandem, area and certifying body all differ, so the efficiencies cannot be compared directly.

Qu et al. report a certified 26.39% on 7.15 mm² (0.0715 cm²) and a certified 25.21% on 99.12 mm² (about 0.99 cm²)Sourced. A 2026 Nature Materials paper (Zhan et al.) reported a certified efficiency of 27.1% for cells using a new molecule, MP3 (the abstract this article checked gives no area)Sourced. Chen et al. (2025) also reported a certified 26.0% for an inverted cell with Me-4PACz formed on NiOSourced.

SAMs are used in tandems too. Hooijer et al. note that SAM-based hole contacts are widely used in perovskite-silicon tandems but still rare in thin-film tandems such as all-perovskite devicesSourced. In one example, the energy levels were tuned step by step through the inductive effect of substituents on the head to match a wide-bandgap (1.68 eV) top-cell perovskite (Luo et al., 2025: 31.1%, certified 30.9%, on 1 cm² in a tandem with a TOPCon bottom cell)Sourced.

5. A materials engineer's view (1): SAMs are cousins of coupling agents

Why this matters for materials engineers: one functional group bonds to the oxide, the other faces the layer above

Put into a materials engineer's language, a SAM is a surface treatment agent with one end that bonds to an inorganic surface and another end that faces an organic partner, in a single molecule. It is the same idea as the silane coupling agents that join glass fibre to resin, or phosphonic-acid surface treatments for metals, and Hooijer et al. do in fact mention silane-based SAMsSourced.

If so, the problems show up in the same places. Hooijer et al. list the main challenges for mass production as reproducibility, control of surface hydroxylation, and defect-free coverage over large areasSourced. That the quality of a coupling treatment is decided by the amount of surface hydroxyl groups on the substrate and how clean it is is common knowledge on the surface-treatment shop floor. How to make the surface condition of ITO or NiOx consistent looks set to become the centre of SAM quality control (our commentary).

The other issue is how to apply it. The same paper says spin coating is not suited to high-throughput manufacturing, and that SAM formation by vapour-phase methods, slot-die coating and roll coating is emerging but not yet standardisedSourced. One molecular layer, over areas of a square metre or more, evenly and fast: continuous coating of a monolayer is a chance for surface-treatment engineers to show what they can do (our commentary).

On the plus side, SAMs follow rough surfaces. Magomedov et al. note that the method suits conformal coating of large-area and textured substrates, with minimal material consumptionSourced. A film one molecule thick is a good match for making a hole layer on top of the pyramid texture of a silicon tandem (our commentary).

6. Weakness 1: incomplete coverage and clumping

Gaps and clumps: patchy coverage and aggregation (concept) Molecules drawn schematically as sticks. Number, spacing and size are not real values (1) Directly on ITO: patchy (2) Molecules aggregate (3) NiO base, better dispersion Uncovered areas can cause shorts and voltage loss Leading to interface losses and lower open-circuit voltage NiO interlayer evens coverage Surfactant curbs aggregation Pale green = NiO layer Note: (1) and the NiO in (3) follow Phung et al. [Ref. 4]; (2) follows Wang et al. [Ref. 5], Du et al. [Ref. 12] and Li et al. [Ref. 11]; the surfactant (CTAB) in (3) follows Du et al. [Ref. 12]. Note: the split into three is this article's own. The round blobs for aggregates are symbols for explanation.
Fig. 3 Concept diagram (vector drawing). The account of each case follows Phung et al. [Ref. 4], Wang et al. [Ref. 5], Li et al. [Ref. 11] and Du et al. [Ref. 12]. The number and spacing of molecules and the shape of the aggregates are all schematic and do not show real coverage or aggregate size.

(1) On ITO, the coverage is not uniform

A 2022 paper in ACS Applied Materials & Interfaces (Phung et al.) observed that a MeO-2PACz SAM covers an ITO substrate only non-uniformly. It says uncovered areas can lead to shunts and lower open-circuit voltage, and reports that inserting a NiO interlayer made by plasma ALD between the ITO and the SAM improved the uniformity and coverage of the SAM, raised the shunt resistance of the devices and narrowed the spread in performance (up to more than 20%)Sourced. It also shows that the SAM is key to the gain in open-circuit voltage and that NiO alone is not enoughSourced.

(2) The molecules clump together

SAMs such as 2PACz tend to aggregate at the buried interface. In 2026 Du et al. suppressed 2PACz aggregation with a surfactant (CTAB) and reported 26.20% on 0.072 cm² and 22.34% for a 22.96 cm² moduleSourced. In 2024 Li et al. suppressed aggregation by co-adsorbing another small molecule, obtaining a certified efficiency of 24.68%Sourced.

7. Weakness 2: acid attacks the layer below; heat and UV break the molecule

Degradation or loss pathwayWhat was reportedSource
Corrosion of the underlying layer by acidThe strong acidity of common phosphonic acid anchors corrodes reactive NiOx and harms stability. Using the milder boric acid as the anchoring group allowed coordination bonding to NiOx while also suppressing aggregation (28.5% in an all-perovskite tandem, with 90% of the initial value kept after 500 hours of maximum power point tracking under 1 sun)Wang et al. (2025)
Breakdown by UV lightCarbazole-based molecules are vulnerable to UV. Photodegradation (N-dealkylation) occurs at non-conjugated linking segmentsZhan et al. (2026)
Breakdown by heatPhosphonic acid anchors are vulnerable to heat. In conjugated structures, heat drives anhydride formationZhan et al. (2026)
Detachment during high-temperature annealingThe 150 °C anneal needed for sequential deposition of the perovskite detaches the SAM and increases non-radiative recombination at the buried interface. Avoided by enabling deposition at 110 °CChen et al. (2025)

All Sourced (Wang et al. [Ref. 5], Zhan et al. [Ref. 7], Chen et al. [Ref. 10]).

With these two degradation pathways in mind, Zhan et al. designed a new molecule, MP3, that combines conjugated and non-conjugated spacers and adds electron-withdrawing substituents. By suppressing UV-driven N-dealkylation and heat-driven anhydride formation, and tuning acid dissociation to strengthen bonding to the substrate, they report that cells kept 93.2% of initial efficiency after 1,000 hours of UV, 91.1% after 1,000 hours at 100 °C, and 94.8% after 2,200 hours of maximum power point tracking at 65 °CSourced.

8. A materials engineer's view (2): designing the acidity of the anchoring group

Conceptual image of a smooth, pale grey-blue flat surface against a dark background, showing an even sheen under light from an angle
Fig. 4 AI-generated concept image. An impression of the underlying surface that the molecules bond to. It does not show a real ITO or NiOx surface, a micrograph, or a product.
Why this matters for materials engineers: sticking well and not damaging the substrate are a tug of war within the same functional group

Phosphonic acid is chosen as the anchoring group because it bonds strongly to oxide surfaces (strong bidentate and tridentate bonds)Sourced. Yet the same property, being an acid, corrodes reactive NiOxSourced. Wang et al. switched to boric acid in order to lower the acidity while keeping the bonding strengthSourced. Zhan et al. likewise say they strengthened bonding to the substrate by tuning the degree of acid dissociationSourced.

This is the same familiar tug of war seen in surface treatment of metals and glass: you want to activate the surface with acid for adhesion, but overdo it and you damage the substrate. The difference here is that the functional group is locked inside a single molecular layer and cannot be rinsed away afterwards (our commentary).

The heat problem can be read the same way. The thermal degradation pathway in which phosphonic acid groups dehydrate and condense into anhydrides is a reaction familiar to chemists who work with phosphorus-based surface treatment agents and flame retardants. Treating the chemistry of the anchoring group as the first variable in molecular design is becoming the short cut to more durable SAMs (our commentary).

9. Our calculation: how many molecules does 1 m² take?

Magomedov et al. list minimal material consumption as one advantage of SAMsSourced. So how much material does it take to cover 1 m² with a single layer of molecules? Let us check the order of magnitude.

Our calculation: covering 1 m² with MeO-2PACz
  • Molecular weight: from the chemical name [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid, the molecular formula is taken as C16H18NO5P; with atomic weights (C 12.011, H 1.008, N 14.007, O 15.999, P 30.974) this gives about 335 g/molOur calculation
  • Assumption: take the density of molecules on the surface as 1 to 3 molecules per nm². This is our own assumption, not a measured value from the papers this article draws on
  • 1 m² = 10¹⁸ nm², so the number of molecules is 1×10¹⁸ to 3×10¹⁸
  • Moles: 1×10¹⁸ ÷ 6.022×10²³ = 1.66×10⁻⁶ mol, up to 4.98×10⁻⁶ mol
  • Mass: × 335 g/mol = about 0.56 to 1.7 mg per m²Our calculation

What this tells us: an ideal monolayer is on the order of a few milligrams per square metre or less. Assumptions and limits: in a real process most of the coating solution does not stay on the substrate (in spin coating it is flung off), so the amount used is far larger than the amount adsorbed. Aggregation or multilayer adsorption would also increase the adsorbed amount (Section 6). This calculation only gives the order of magnitude of the lower bound for what stays in the film; it is not an estimate of material cost.

How much it takes to cover 1 m² with one layer of molecules (our calculation) Example: MeO-2PACz (about 335 g/mol), converted with an assumed packing density about 335 g/mol (molecular weight) C16H18NO5P Calculated from the chemical name 1 to 3 molecules per nm² 10¹⁸ to 3×10¹⁸ per m² Our assumption (not a measurement) 0.56 to 1.7 mg/m² (left in the film) Actual usage is higher Our calculation An ideal monolayer is on the order of a few mg per m² or less Note: the chemical name follows Phung et al. [Ref. 4]. Molecular formula, weight and mass are this article's calculation. Note: 1 to 3 molecules/nm² is our assumption, not a measured value. Aggregation and multilayers are not included. Note: most coating solution does not stay on the substrate, so this is not an estimate of usage or material cost.
Fig. 5 Drawing that includes our calculation (vector drawing). The chemical name of MeO-2PACz follows Phung et al. [Ref. 4]. The molecular formula, molecular weight (about 335 g/mol) and mass per square metre (about 0.56 to 1.7 mg) were calculated by this article and are not published figures. The packing density of 1 to 3 molecules per nm² is our own assumption.

10. Strengths and open problems

Strengths and challenges of self-assembled monolayers (this article's framing) Strengths Challenges No dopant needed Very little parasitic absorption Follows textured surfaces conformally Energy levels tuned through head design What stays in the film is on the order of mg/m² Certified 27.1% reported in a single junction Patchy coverage on ITO Molecules tend to aggregate Acidic anchors corrode NiOx Vulnerable to UV, heat and hot annealing No standard large-area coating method yet Control of surface hydroxyls and reproducibility Note: items follow the papers [Refs. 1 to 12] and our calculation (Section 9). Note: the split into two groups is this article's own and is not an established industry assessment.
Fig. 6 Concept diagram (vector drawing). Each item follows the papers [Refs. 1 to 12] and this article's calculation (Section 9). Sorting them into strengths and challenges is this article's own framing, not an established industry assessment.

(1) The standard coating method for mass production is not settled

Hooijer et al. say that SAM formation by vapour-phase methods, slot-die coating and roll coating is emerging but not standardisedSourced. Which method will become the production standard could not be confirmed at the time of our researchNot yet confirmed.

(2) The durability figures come from accelerated tests

Figures such as 1,000 hours of UV, 1,000 hours at 100 °C and 2,200 hours of maximum power point tracking are results of accelerated tests in the laboratorySourced. How many years the cells last outdoors could not be confirmed in the primary sources within the scope of this articleNot yet confirmed.

(3) What this article does not cover

The synthesis cost and market price of SAM molecules, and volume supply by particular companies, are not covered here because what can be confirmed in primary sources is limited.

The article in summary
  • A SAM is a hole-extraction layer one molecule thick, first used in a p-i-n cell in 2018 (17.8%)Sourced
  • The molecule has three parts: head, linker and anchoring group. The 2PACz family is carbazole + alkyl chain + phosphonic acidSourced
  • On ITO it does not cover uniformly, and it tends to aggregate. There are examples of improvement with a NiO interlayer, a surfactant or co-adsorptionSourced
  • Acidic anchors corrode NiOx, form anhydrides with heat and break down under UV. The chemistry of the anchoring group is the key to durabilitySourced
  • An ideal monolayer amounts to about 0.56 to 1.7 mg per m² (packing density assumed)Our calculation
  • A SAM is a surface treatment on the same principle as a coupling agent; control of surface hydroxyls and continuous coating are the issues for mass production (commentary)

11. Glossary

Self-assembled monolayer (SAM)
A film one molecule thick, formed when molecules spontaneously bond to and line up on a substrate surface.
Anchoring group
The functional group in the molecule that bonds to the underlying surface, such as phosphonic acid.
Linker (spacer)
The part joining the head to the anchoring group, such as an alkyl chain or phenylene.
Head
The part facing the layer above (the perovskite), such as carbazole.
Phosphonic acid
An acid carrying a −PO(OH)2 group. Bonds strongly to oxide surfaces.
Carbazole
A nitrogen-containing aromatic compound with three rings. Used as a backbone that carries holes readily.
2PACz / MeO-2PACz / Me-4PACz
Representative SAM molecules that join carbazole to phosphonic acid through an alkyl chain.
Parasitic absorption
Light absorbed by layers that do not contribute to generating power.
Coverage
The fraction of the substrate surface area covered by molecules.
Aggregation
Molecules gathering into clumps, which prevents a uniform monolayer.
Co-adsorption
Adsorbing two or more kinds of molecule onto a surface at the same time.
N-dealkylation
A reaction in which an alkyl group bonded to nitrogen comes off. Can be caused by UV light.
Silane coupling agent
A surface treatment agent that joins inorganic surfaces to organic materials. A molecule built on the same idea as a SAM.

12. References (primary sources)

  1. Magomedov, A. et al. “Self-Assembled Hole Transporting Monolayer for Highly Efficient Perovskite Solar Cells”, Advanced Energy Materials 8, 1801892 (2018) https://doi.org/10.1002/aenm.201801892
  2. Al-Ashouri, A. et al. “Conformal monolayer contacts with lossless interfaces for perovskite single junction and monolithic tandem solar cells”, Energy & Environmental Science 12, 3356–3369 (2019) https://doi.org/10.1039/c9ee02268f
  3. Al-Ashouri, A. et al. “Monolithic perovskite/silicon tandem solar cell with >29% efficiency by enhanced hole extraction”, Science 370, 1300–1309 (2020) https://doi.org/10.1126/science.abd4016
  4. Phung, N. et al. “Enhanced Self-Assembled Monolayer Surface Coverage by ALD NiO in p-i-n Perovskite Solar Cells”, ACS Applied Materials & Interfaces 14, 2166–2176 (2022, open access) https://doi.org/10.1021/acsami.1c15860
  5. Wang, J. et al. “Less-acidic boric acid-functionalized self-assembled monolayer for mitigating NiOx corrosion for efficient all-perovskite tandem solar cells”, Nature Communications 16, 4148 (2025, open access) https://doi.org/10.1038/s41467-025-59515-6
  6. Hooijer, R. et al. “Why more junctions do not yet deliver: interconnection challenges in perovskite multijunction solar cells”, Energy & Environmental Science 19, 4582–4596 (2026, open access) https://doi.org/10.1039/d6ee01631f
  7. Zhan, L. et al. “UV and thermally stable hole-selective contacts with enhanced assembly density for inverted perovskite solar cells”, Nature Materials (2026) https://doi.org/10.1038/s41563-026-02619-1
  8. Qu, G. et al. “Self-assembled materials with an ordered hydrophilic bilayer for high performance inverted Perovskite solar cells”, Nature Communications 16, 86 (2025, open access) https://doi.org/10.1038/s41467-024-55523-0
  9. Luo, Y. et al. “Inductive effects in molecular contacts enable wide-bandgap perovskite cells for efficient perovskite/TOPCon tandems”, Nature Communications 16, 4516 (2025, open access) https://doi.org/10.1038/s41467-025-59896-8
  10. Chen, M. et al. “Low-temperature sequential deposition for efficient inverted perovskite solar cells”, Nature Communications 16, 5746 (2025, open access) https://doi.org/10.1038/s41467-025-61144-y
  11. Li, D. et al. “Co-adsorbed self-assembled monolayer enables high-performance perovskite and organic solar cells”, Nature Communications 15, 7605 (2024, open access) https://doi.org/10.1038/s41467-024-51760-5
  12. Du, K. et al. “Anti-aggregation self-assembled monolayers enable high-performance and scalable perovskite solar cells”, Nature Communications 17, 1472 (2026, open access) https://doi.org/10.1038/s41467-025-68207-0

13. Claim-to-source audit

Claim in the textBasisLabel
First use of a SAM as a dopant-free hole-selective contact in a p-i-n cell, with 17.8% efficiency, an average fill factor of close to 80% and parasitic absorption too small to detect. The substrate simply dipped in a solution of V1036, bonding to ITO through a phosphonic acid anchoring group. Suitability for conformal coating of large-area and textured substrates, with minimal material consumptionMagomedov et al. (Advanced Energy Materials, 2018). Reference 1 https://doi.org/10.1002/aenm.201801892Sourced
That a paper using monolayer hole-selective contacts in single-junction and monolithic tandem cells was published in EES in 2019 (based on the paper's title and abstract; no values in the text are taken from it)Al-Ashouri et al. (Energy & Environmental Science, 2019). Reference 2 https://doi.org/10.1039/c9ee02268fSourced
A methyl-substituted carbazole SAM used as the hole-selective layer, speeding hole extraction and reducing non-radiative recombination at the interface, with a certified efficiency of 29.15% for a silicon tandemAl-Ashouri et al. (Science, 2020). Reference 3 https://doi.org/10.1126/science.abd4016Sourced
The chemical name of MeO-2PACz. That a MeO-2PACz SAM covers ITO only non-uniformly and uncovered areas can cause shunts and low open-circuit voltage. That a plasma-ALD NiO interlayer improved SAM uniformity and coverage, raised shunt resistance and narrowed the performance spread (up to more than 20%), and that the SAM is key to the gain in open-circuit voltagePhung et al. (ACS Applied Materials & Interfaces, 2022). Reference 4 https://doi.org/10.1021/acsami.1c15860Sourced
That strongly acidic phosphonic acid anchors corrode reactive NiOx and harm stability. That SAM aggregation causes interfacial losses and insufficient open-circuit voltage. That using the milder boric acid as the anchoring group allowed coordination bonding to NiOx and also suppressed aggregation. 28.5% for a two-terminal all-perovskite tandem, with 90% of the initial value kept after 500 hours of maximum power point tracking under 1 sunWang et al. (Nature Communications, 2025). Reference 5 https://doi.org/10.1038/s41467-025-59515-6Sourced
That SAMs on a TCO form covalent or ionic bonds and make stable, dense interfacial layers. Strong bidentate and tridentate bonding of phosphonic acid, and Si–O–Si cross-linking in silane-based SAMs with a risk of hydrolysis. That SAMs are widely used in silicon tandems but still rare in thin-film tandems such as all-perovskite devices. That spin coating is not suited to high-throughput manufacturing and that vapour-phase, slot-die and roll-coating methods are emerging but not standardised. Reproducibility, control of surface hydroxylation and defect-free large-area coverage as the main challengesHooijer et al. (Energy & Environmental Science, 2026). Reference 6 https://doi.org/10.1039/d6ee01631fSourced
The UV vulnerability of carbazole-based molecules and the thermal instability of phosphonic acid anchors. Photodegradation (N-dealkylation) at non-conjugated linking segments and heat-driven anhydride formation in conjugated structures. MP3, combining conjugated and non-conjugated spacers with electron-withdrawing substituents, with bonding to the substrate strengthened by tuning acid dissociation. A certified efficiency of 27.1%. 93.2% after 1,000 hours of UV, 91.1% after 1,000 hours at 100 °C, and 94.8% after 2,200 hours of maximum power point tracking at 65 °CZhan et al. (Nature Materials, 2026). Reference 7 https://doi.org/10.1038/s41563-026-02619-1Sourced
The advantages of SAMs (tunable energy levels, low synthesis cost, low parasitic absorption, passivation of defects in the perovskite and the TCO). The description of the molecule as head, linker and anchoring group. Certified efficiencies of 26.39% (7.15 mm²) and 25.21% (99.12 mm²)Qu et al. (Nature Communications, 2025). Reference 8 https://doi.org/10.1038/s41467-024-55523-0Sourced
Stepwise tuning of SAM energy levels through inductive effects to match a 1.68 eV wide-bandgap cell. 31.1% (certified 30.9%) on 1 cm² in a tandem with TOPConLuo et al. (Nature Communications, 2025). Reference 9 https://doi.org/10.1038/s41467-025-59896-8Sourced
The chemical name of Me-4PACz and the configuration with Me-4PACz formed on NiO. That the 150 °C anneal in sequential deposition detaches the SAM and increases non-radiative recombination, deposition at 110 °C, and a certified efficiency of 26.0%Chen et al. (Nature Communications, 2025). Reference 10 https://doi.org/10.1038/s41467-025-61144-ySourced
Suppression of 2PACz aggregation with a co-adsorbed molecule, giving over 25% (certified 24.68%) in p-i-n cellsLi et al. (Nature Communications, 2024). Reference 11 https://doi.org/10.1038/s41467-024-51760-5Sourced
The chemical name of 2PACz. That SAMs tend to aggregate at the buried interface. Suppression of aggregation with the surfactant CTAB, giving 26.20% on 0.072 cm² and 22.34% for a 22.96 cm² moduleDu et al. (Nature Communications, 2026). Reference 12 https://doi.org/10.1038/s41467-025-68207-0Sourced
The molecular formula C16H18NO5P and molecular weight of about 335 g/mol for MeO-2PACz. About 0.56 to 1.7 mg per m² under an assumed packing density of 1 to 3 molecules per nm²Our calculation. The formula was derived by this article from the chemical name and the weight from atomic weights. The packing density is our assumption, not a measured value from the papers. Aggregation, multilayer adsorption and losses of coating solution are not includedOur calculation
The standard coating method for SAMs in mass production, and long-term outdoor durabilityNot stated because they could not be confirmed in the primary sources within the scope of this article (commentary by this article)Not yet confirmed
How to read the short names (PA, Cz, the number, the substituent) and the breakdown in the table into head, linker and anchoring group. Reading SAMs as the same idea as coupling agents and phosphonic-acid surface treatments. The reading that control of surface hydroxyls will be central to quality control. Treating continuous coating of monolayers as a surface-treatment challenge. The framing of a tug of war between sticking well and not damaging the substrate. Linking anhydride formation to the chemistry of phosphorus-based surface treatment agents and flame retardants. The classification of weaknesses into coverage, aggregation, acid, heat and UV, and the sorting into strengths and challengesThis article's own framing and commentary based on published content. Not views expressed by the researchersCommentary
That Figs. 1, 2, 3, 5 and 6 are explanatory drawings, and that the hero image and Fig. 4 are AI-generated imagesA note by this article (commentary)Commentary

Last updated 25 September 2026. Sources are limited to primary material (peer-reviewed papers). Every efficiency value is given with whether it is certified and, where it could be confirmed, its area. The cell area for the certified 27.1% of Zhan et al., the standard coating method for SAMs in mass production, long-term outdoor durability, and the price and volume supply of SAM molecules are not stated, because they could not be confirmed in published primary sources. All figures are for explanation. Figs. 1, 2, 3, 5 and 6 are vector drawings, and the hero image and Fig. 4 are AI-generated images; none of them shows a real cross-section, micrograph, molecular structure or physical product.

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