Lead and Tin Perovskites
In the quest for cleaner energy, scientists are engineering materials atom by atom to revolutionize how we harness sunlight.
Imagine a solar cell so thin it could be painted onto surfaces, yet so efficient it rivals traditional silicon panels. This isn't science fiction—it's the promise of hybrid halide perovskites, a class of materials that has taken the solar research community by storm. At the heart of these remarkable materials lies an elegant atomic architecture that determines their exceptional ability to convert sunlight into electricity. The precise arrangement of atoms at the surface of these perovskites holds the key to both unprecedented efficiency and lingering challenges that scientists are working to overcome.
All hybrid halide perovskites share the same fundamental ABX₃ crystal structure—a three-dimensional lattice where each component plays a specific role in the material's overall properties 5 6 .
Organic cations (CH₃NH₃⁺, HC(NH₂)₂⁺) or inorganic cations (Cs⁺)
Lead (Pb²⁺) or Tin (Sn²⁺) cations
Halide anions (I⁻, Br⁻, Cl⁻)
In this arrangement:
This ingenious configuration creates what materials scientists call a "defect-tolerant" structure, meaning the material can still perform efficiently even with minor imperfections that would cripple other semiconductors 6 .
| Position | Elements/Molecules | Role in Structure |
|---|---|---|
| A (cation) | Methylammonium (CH₃NH₃⁺), Formamidinium (HC(NH₂)₂⁺), Cesium (Cs⁺) | Stabilizes crystal structure, fills voids |
| B (metal) | Lead (Pb²⁺), Tin (Sn²⁺) | Forms octahedral core with halides, determines electronic properties |
| X (halide) | Iodide (I⁻), Bromide (Br⁻), Chloride (Cl⁻) | Coordinates with metal cations, influences bandgap |
While lead-based perovskites have achieved remarkable solar conversion efficiencies exceeding 26%, the toxicity of lead has motivated an urgent search for safer alternatives 6 8 . Tin has emerged as the most promising successor, but each material brings distinct advantages and challenges to the table.
Lead-based perovskites boast exceptional optoelectronic properties that make them nearly ideal for photovoltaics. They feature:
These outstanding properties explain why lead-halide perovskites have achieved such impressive efficiencies in both single-junction and tandem solar cell configurations 6 8 .
Tin-based perovskites represent the most promising lead-free alternative, with their own set of advantages and challenges 1 7 :
| Property | Lead-Based | Tin-Based |
|---|---|---|
| Optimal Bandgap | ~1.55 eV (MAPbI₃) | ~1.3-1.4 eV (MASnI₃) |
| Toxicity | High concern | Low concern |
| Stability | Moderate | Poor (oxidizes easily) |
| Carrier Mobility | High | Very high (~585 cm²/V·s for CsSnI₃) |
| Best PCE | >26% | ~17% (pure tin), >29% (tin-lead tandem) |
The surfaces of perovskite materials are their most vulnerable points, where structural integrity and performance degradation begin. For lead-based perovskites, surface instability often manifests as:
Tin-based perovskites face even greater surface challenges, particularly tin segregation and oxidation. As one recent study noted, "Sn segregation at the film surface disrupts energy band alignment, increases surface defect density, and intensifies non-radiative recombination. This Sn-rich capping layer is also highly prone to oxidation, further undermining device stability" .
A recent landmark study published in Nature Communications in 2025 addressed one of the most persistent challenges in tin-based perovskites: achieving uniform, stable films at the thicknesses required for high-performance solar cells .
First, they observed that conventional dimethylformamide (DMF)/dimethyl sulfoxide (DMSO) solvent systems failed to properly coordinate with SnI₂ at high precursor concentrations, leading to Sn-rich colloids that caused non-uniform crystallization .
They developed a ternary solvent system (TSS) by introducing trichloromethane (TCM) to the conventional DMF/DMSO mixture .
Using Fourier-transform infrared spectroscopy (FTIR) and ¹³C nuclear magnetic resonance (NMR), they confirmed that TCM preferentially coordinates with SnI₂ through both halogen and hydrogen bonding, suppressing Sn-rich phase formation .
They fabricated micron-thick Sn-Pb perovskite films using both conventional and TSS approaches, comparing crystallization behavior, film uniformity, and optoelectronic properties .
The TSS approach yielded dramatic improvements:
These material improvements translated directly to superior device performance, with the TSS-enabled Sn-Pb absorbers achieving efficiencies of 24.2% in single-junction cells and 29.3% in all-perovskite tandem devices .
| Parameter | Conventional Solvent | TSS Approach |
|---|---|---|
| Carrier Diffusion Length | Limited (~2-3 μm) | ~11 μm |
| Sn Segregation | Pronounced | Significantly suppressed |
| Film Uniformity | Non-uniform, voids | Uniform, dense |
| Single-Junction PCE | <22% | 24.2% |
| Tandem Cell PCE | <27% | 29.3% |
Working with hybrid halide perovskites requires specific materials and reagents, each serving distinct purposes:
PbI₂, SnI₂ - Provide the metal cations and halide anions that form the perovskite framework. SnF₂ is often added to suppress Sn²⁺ oxidation 3 .
MAI, FAI - Source the 'A' site organic cations in the perovskite structure .
DMF, DMSO, TCM - Dissolve precursors and control crystallization kinetics. DMF/DMSO mixtures are standard, with additives like TCM improving coordination .
Chlorobenzene, Diethyl Ether - Added during film processing to trigger uniform perovskite crystallization .
PEAI, RACl - Organic salts that form protective layers or integrate into the perovskite to enhance stability 6 .
The path forward for hybrid halide perovskites involves addressing several key challenges while building on recent breakthroughs:
Developing advanced encapsulation techniques and protective layers to shield perovskite surfaces from environmental stressors 8 .
Continued innovation in tin-based formulations and lead-tin mixtures that minimize environmental impact without sacrificing performance 1 .
Adapting laboratory successes to industrial-scale production through printing and coating techniques compatible with large-area substrates 2 .
As research progresses, the atomic-level understanding of perovskite surfaces and their electronic properties will continue to drive efficiency and stability improvements. From the fundamental ABX₃ structure to sophisticated solvent engineering strategies, each scientific advance brings us closer to realizing the full potential of these remarkable materials—potentially transforming how we harness solar energy and power our world.
For further reading, the open-access article "Tin-based halide perovskite materials: properties and applications" in Chemical Science provides excellent additional information on lead-free alternatives 1 .