Perovskite research moves from single additives to multifunctional chemistry

Zwitterions as multifunctional additives

Zwitterions are neutral molecules that carry positive and negative charges. The review says the dual charge does more than passivate defects.

The review says one molecular unit can handle defect passivation, crystallization modulation and interfacial energy-level tuning, a combination the authors say conventional Lewis acid/base passivators and single ionic additives do not offer. That matters because perovskite cells still lose efficiency to defects and degrade under heat and humidity, so each additive has to improve performance and durability at once. The reported efficiencies remain lab-scale. Neither commercial module lifetimes nor manufacturing yields appear in the published results.

Betaine-type zwitterions are the most extensively studied, the review says. In tin perovskites, the amino acid L-asparagine raised cell efficiency from 10.54% to 13.31%.

Formamidine sulfinic acid enabled 22.06% in a wide-bandgap device. The authors say the effectiveness of these mechanisms depends on molecular structure, how the compound is incorporated and where it sits in the device. Liquid-type zwitterions could address poor solubility, they add.

Automation and salt additives target film formation

At the University of Osaka, researchers built an automated platform that watches perovskite film formation as it happens. It measures color changes on a subsecond timescale and resolves the motion and impact of antisolvent droplets within a few milliseconds. Asia Research News reported on 2 November that the system, described in ACS Nano, pairs those measurements with machine learning. The team then used the analysis to guide fabrication of a lead-based device that reached 24.4% power conversion efficiency.

“We want to move beyond trial and error by measuring what happens to the film while it is actually forming,” lead author Ryosuke Kado said.

Separately, researchers at Argonne National Laboratory used two salts, zinc bromide and methylammonium chloride, to lower the melting point of the perovskite precursors. The film briefly liquefies, then atoms settle into a more uniform structure. Nanowerk reported on 30 October that the method, published in Science, produced a solar cell at 26.5% efficiency and an LED at 26.1% external quantum efficiency. “Defects have been the bottleneck for perovskites for almost a decade,” study author Yanqi Luo said.

Stability gets a lithium-removal step

Stability is the other half of the problem. Scientists at the Korea Institute of Energy Research used nickel oxide to pull lithium ions out of the hole transport layer, then removed them by filtration, pv magazine reported on 27 October. The champion cell reached 25.24% efficiency and kept more than 90% of its initial efficiency after 500 hours of continuous operation. It retained 95% under damp-heat testing at 85 C and 85% relative humidity. The process enables oxidation of spiro-OMeTAD in less than five seconds without the additive tBP, and conductivity in the hole transport layer rose by a factor of 2.5.

The efficiency gap remains

Not every result lands in the same range. A Bioengineer.org report on 26 October described a caesium tin iodide cell that reached 10.76% after a model-guided redesign, up from 8.98% for an unoptimised counterpart. Tin perovskites avoid lead but oxidise in air, which has kept them behind their lead-based rivals.

All-perovskite tandem devices are further ahead. Real devices of that class have reached 30.1%, against a theoretical maximum near 45%, Bioengineer.org reported on 30 October.

A simulation study from Huazhong University of Science and Technology projected 31.13% for a tandem cell with serrated front and buried interfaces, a 3.41% increase over the flat baseline, Bioengineer.org reported on 30 October. Simulations are not devices. The gap between the two numbers is where the commercial argument still sits.