How does repeated substrate reuse affect carrier transport in perovskite solar cells? Optimize recycling with lab insights

Repeated substrate reuse generally causes a gradual loss of photovoltaic performance because residual lead iodide accumulates at the mesoporous TiO₂/perovskite interface. After the degraded perovskite is rinsed away with a solvent such as DMF, some PbI₂ remains bound to the TiO₂ surface. This residue can hinder carrier extraction and reduce the available surface area for loading fresh perovskite, producing lower short-circuit current density (Jsc) and open-circuit voltage (Voc) over successive recycling cycles.

Reusing substrate templates can reduce material waste and fabrication cost, but it is not performance-neutral. The key limitation is progressive interfacial contamination: residual PbI₂ makes fresh perovskite reloading less complete and disrupts charge transport through the TiO₂/perovskite contact.

Why Repeated Reuse Changes the Interface

Residual PbI₂ remains after solvent rinsing

In a recycled monolithic device, the degraded perovskite layer is removed using an organic solvent such as DMF. This process can clear much of the bulk film while leaving lead iodide bound within or on the surface of the mesoporous TiO₂.

The residue is therefore not equivalent to a fully restored TiO₂ template. It becomes part of the interface encountered during deposition of the next perovskite layer.

Fresh perovskite cannot fully restore the original structure

Residual PbI₂ may not readily convert back into perovskite during the next deposition cycle. As a result, portions of the TiO₂ surface and mesoporous network are no longer available for effective perovskite formation.

This reduces the effective contact area between the electron-transport material and the newly deposited absorber.

Carrier extraction becomes less effective

The TiO₂/perovskite interface is central to electron extraction in a monolithic perovskite solar cell. A persistent PbI₂-rich interfacial layer can hinder carrier movement across that junction and increase the difficulty of extracting photogenerated electrons.

The practical consequence is reduced carrier collection, particularly when the residue becomes more extensive over multiple reuse cycles.

How the Electrical Performance Declines

Short-circuit current density decreases

A lower Jsc indicates that fewer photogenerated carriers are being collected under short-circuit conditions. In recycled substrates, this is consistent with incomplete perovskite reloading, reduced interfacial area, and poorer transport across the TiO₂/perovskite contact.

The active layer may still appear visually present while providing less electrically effective contact with the underlying transport structure.

Open-circuit voltage decreases

The accumulation of residual material can also reduce Voc. This reflects a deterioration in the conditions required to maintain a high photovoltage, including less effective carrier extraction and potentially greater interfacial recombination.

The decline in Voc is important because it shows that reuse affects more than absorber loading alone; it also changes the quality of the electronic interface.

Power conversion efficiency declines cumulatively

Because both Jsc and Voc can decrease, the overall power conversion efficiency declines progressively with recycling. The trend is cumulative rather than necessarily catastrophic after a single reuse cycle.

This makes cycle number an essential experimental variable when assessing whether template recycling is genuinely cost-effective.

What Researchers Should Control During Processing

Solvent rinsing conditions

The cleaning protocol should be treated as a controlled processing step, not merely as a removal operation. Researchers should record the solvent used, exposure time, rinsing sequence, drying conditions, and any variation in the process between cycles.

More aggressive rinsing may improve removal of residual material, but it must also be evaluated for its effect on the mesoporous TiO₂ structure and the underlying transparent conductive oxide.

Completeness of perovskite removal

A substrate may look clean while still carrying chemically bound PbI₂. Visual inspection alone is therefore insufficient for judging whether the template is ready for another deposition cycle.

The relevant question is whether the previous perovskite layer and its decomposition products have been removed without leaving an electrically obstructive residue.

Mesoporous TiO₂ surface accessibility

The mesoporous layer provides the surface area needed for intimate contact with the perovskite. Repeated processing should be evaluated for whether pores remain accessible and whether residue progressively blocks or coats the available interface.

A reduction in accessible surface area can limit fresh perovskite infiltration even when the nominal deposition recipe remains unchanged.

Consistency of fresh-film deposition

Reloading conditions should be kept constant across cycles, including precursor preparation, deposition parameters, drying, and conversion conditions. Otherwise, changes in film quality may be incorrectly attributed to substrate recycling.

Researchers should distinguish between template-induced degradation and ordinary deposition variability.

Cycle-by-cycle electrical testing

Each recycled device should be evaluated using the same testing conditions and measurement sequence. Tracking Jsc, Voc, fill factor, and power conversion efficiency as a function of reuse cycle helps identify whether degradation begins primarily through current loss, voltage loss, or both.

This is especially important when comparing cleaning methods or deciding how many reuse cycles are acceptable.

How to Interpret the Transport Mechanism

The issue is not simply “more PbI₂ is always harmful”

PbI₂ can serve beneficial passivation functions in some perovskite architectures. However, the relevant issue here is persistent residual PbI₂ left on the TiO₂ template after recycling, where it can obstruct fresh perovskite formation and carrier transfer.

Its effect depends on its location, continuity, and interaction with the mesoporous interface—not merely on its chemical identity.

Interfacial obstruction and incomplete loading act together

The performance loss has two linked components. Residual PbI₂ can impede carrier transport directly, while also reducing the surface area and pore volume available for effective perovskite reloading.

This combination explains why recycling can lower both photocurrent and photovoltage over time.

Understanding the Trade-offs

Lower material consumption versus lower device performance

Substrate reuse can reduce consumption of transparent conductive oxide glass, mesoporous TiO₂ templates, and associated fabrication resources. That benefit must be weighed against the gradual loss in efficiency and the additional processing needed to restore performance.

A recycled substrate is economically attractive only if the savings exceed the value lost through reduced output and extra quality-control steps.

More cleaning versus structural damage

Increasing the intensity or duration of cleaning may remove more residual perovskite-related material. However, excessive processing could damage or alter the mesoporous transport layer or other substrate components.

Cleaning should therefore be optimized for residue removal with structural preservation, rather than for maximum chemical treatment.

Recycling count versus reproducibility

Allowing many reuse cycles may improve nominal material efficiency but make device performance less uniform. Variability in residual PbI₂, pore accessibility, and fresh-film coverage can complicate comparisons between devices.

A defined maximum reuse count may be more scientifically useful than unrestricted recycling.

Apparent efficiency versus true process efficiency

A recycled device that retains acceptable efficiency may still require longer cleaning, more inspection, or more failed reloads. Process evaluation should include yield, cycle time, consumables, and measurement effort—not only the efficiency of the best-performing cell.

Making the Right Choice for Your Goal

The appropriate recycling strategy depends on whether the priority is maximum efficiency, process development, or material utilization.

• If your primary focus is maximum photovoltaic performance: Use stringent substrate-quality screening and limit reuse once residual PbI₂ begins to reduce Jsc or Voc.
• If your primary focus is process optimization: Compare cleaning protocols systematically while tracking cycle number, residue, perovskite reloading quality, and all key device parameters.
• If your primary focus is material cost-efficiency: Quantify the efficiency decline and added processing burden against the savings from reusing the substrate.
• If your primary focus is reproducible research: Keep solvent treatment, drying, deposition, and testing conditions constant across cycles and report the reuse history of every substrate.

Substrate recycling is viable only when interfacial residue, carrier transport, and cycle-dependent performance are measured together rather than treated as separate processing concerns.

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