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Soochow and LONGi break the tandem cell's buried-interface tradeoff with speckled zirconia
A Soochow University and LONGi team set discrete zirconia nanoparticles under the perovskite and certified an open-circuit voltage of 2.014 V. The 34.0% efficiency is a lab figure, and the certified steady-state number is 33.5%.
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What happened
- A perovskite-silicon tandem cell from Soochow University and the LONGi Central R&D Institute recorded an independently certified open-circuit voltage of 2.014 V, among the highest ever reported for the device type.
- The same work reports a laboratory power conversion efficiency of 34.0%, with certified testing confirming a steady-state efficiency of 33.5%.
- Encapsulated cells held 84% of their starting efficiency after 2,000 hours under continuous simulated sunlight at room temperature.
Compiled by The Product DeskSomething wrong?How this is made
Why it matters
- decision Any tandem programme that has been treating the buried interface as a physical limit now has to argue against a published workaround, and the argument moves to area and yield.
- constraint For anyone modelling when tandem panels become specifiable, the binding evidence is now stability, and 2,000 hours of light soak is the longest window on the record.
- capability Other labs can test the idea by adding a nanoparticle dispersion beneath a monolayer they already use, without redesigning the device stack.
The certified voltage came from a different cell than the 34.0% device. Interesting Engineering reports the press release leading on an independently certified open-circuit voltage of 2.014 V [1]. Neither cell area nor a module result is reported. The 34.0% device is listed separately at 1.997 V, with a current density of 20.36 mA/cm2 and a fill factor of 83.62% [13], 17 millivolts short of the certified figure [2]. Multiply those three parameters and the product is 34.0 milliwatts per square centimetre, matching the stated efficiency [1].
The problem being attacked is narrow. Textured silicon pulls more light into the stack, and it grows a smooth perovskite film badly [19][5]. Holes have to leave through the buried interface, and that is where charge gets trapped and lost to non-radiative recombination [6]. Earlier interface treatments cut those losses and laid down an insulating barrier that slowed the current [7]. Soochow's answer was to stop covering the surface: separate monoclinic zirconia nanoparticles sit between the conductive oxide and the molecular monolayer [8]. Those particles change the surface energy so the perovskite solution spreads evenly, which the team reports as dense, void-free films with larger crystal grains [9].
"Second, the discrete nanoparticles form nanoscale localized contacts at the interface," the researchers said in a press release. "The zirconia regions provide field-effect passivation that suppresses non-radiative recombination, while the exposed monolayer pathways preserve efficient hole extraction." [10]
Time-resolved measurements put carrier lifetime at 2.81 microseconds after treatment against 1.46 before, a 92% increase [12][3]. Zirconia's high dielectric constant also shields the interface from electrical fluctuations and prevents charge build-up, and chemical tests found Zr-O-P bonds anchoring the particles to the monolayer [11]. The work was co-led by Prof Jiang Liu, Prof Xiaohong Zhang and Dr Hongbo Mo at Soochow University with Dr Bo He at LONGi [16].
Under the 34% headline sits one fabrication step that lets passivation and hole extraction both work at the buried interface, and the press release calls it "a practical strategy for developing more efficient and durable perovskite/silicon tandem solar cells" [18].
Ask of this record, and of the next one, which figure was certified and which was the champion cell: here they sit half a percentage point apart, 33.5% against 34.0% [5]. Then ask how far the durability evidence reaches: the encapsulated cells lost 16% of their output over the equivalent of 83 days of unbroken illumination [4].
What to watch
- Whether the next paper on this interface recipe reports cell area and a module-scale result.
- A light-soak test longer than 2,000 hours, or one run at elevated temperature, on the same stack.
- Whether another group reproduces the 2.014 V open-circuit voltage, or LONGi moves the zirconia step to a pilot line.