Key Findings
The LIMNO lab at EPFL, led by Kevin Sivula, has created the first lead-free layered double perovskite that can function in water. The material, (NDI-dH)₂AgBiI<0xE2><0x82><0x88>, demonstrated a photocurrent of 0.25 mA/cm² at +1.0 V against a reversible hydrogen electrode under one-sun illumination when used as a photoanode in a water-based electrolyte containing a sacrificial electron donor.
Technical Details
The stability and performance of the material are attributed to the use of naphthalene diimide, a bulky, water-repelling organic spacer. Technical comparisons against spacers using benzene-based or simple aliphatic chains revealed the following:
- In-plane carrier mobility was threefold higher.
- Trap density was an order of magnitude lower.
- Structural integrity was maintained during accelerated testing (24 hours at 30°C and 80% relative humidity), whereas the other two versions bleached and lost their layered structure.
While the bare film degraded gradually during operation, the addition of a hole-transporting polymer overlayer allowed the device to run for more than an hour, though this resulted in some loss of photocurrent. Notably, the organic spacer does not merely serve as a scaffold; it also absorbs light, contributing to the overall photocurrent.
Background & Context
Layered hybrid double perovskites are considered promising for optoelectronic and solar applications. However, their inherent sensitivity to water has historically prevented their application in environments where semiconductors must touch liquids, such as in biosensors or the production of solar fuels.
Significance & Outlook
The results indicate that spacer engineering is a viable pathway toward creating stable, lead-free perovskite photoelectrodes. By optimizing the organic components to repel water while maintaining electronic properties, researchers can expand the utility of lead-free perovskites into aqueous environments.
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