Italian startup develops 20.7%-efficient mini perovskite solar modules with 99.6% geometrical fill factor

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Italian perovskite specialist Solertix, a unit of Italy-based solar manufacturer FuturaSun, has fabricated mini perovskite solar panels with an active surface of 2.6 cm2 and a power conversion efficiency of 20.7%.

“We optimized the laser processes to fabricate the interconnects that are used to go from cells to modules,” Solertix CTO, Francesco Di Giacomo, told pv magazine. “Since the area used for the interconnects does not produce energy, we have introduced a new layout to minimize this area without introducing other types of losses. The factor that takes this into account is the geometrical fill factor (GFF) which describes the ratio between active area and the sum of active area and interconnects, and we reached a record of around 99.6%, while in literature it is difficult to go beyond 95%.”

In the research paper “Beyond 99.5% Geometrical Fill Factor in Perovskite Solar Minimodules with Advanced Laser Structuring,” written in cooperation with scientists of the University of Rome Tor Vergata, of which Solertix is a spin-off, the Italian startup explained that, when upscaling from perovskite cells to modules, losses can be caused by layer inhomogeneity loss, P2 ohmic loss, shunts across P1 and P3, and sheet resistance loss.

The so-called P1, P2, and P3 scribes correspond to the three scribing steps of the process for building the monolithic interconnections that add voltages between cells in modules. The P1 and P3 steps are aimed at isolating the back contact layers of neighboring cells and the P2 step creates an electrical path between the back contact of a cell with the front contact of an adjacent cell. The P3 step, in particular, is often a source of undesired effects such as back contact delamination, flaking, or poor electrical isolation, due to residues that remain in the trench.

The module was built with three cells, each with an area of 0.87 cm2. The cells were all designed with a substrate made of glass and indium tin oxide, a hole-transporting material relying on poly(triarylamine) (PTAA), a perovskite absorber, an electron transport layer based on phenyl-C61-butyric acid methyl ester (PCBM), a bathocuproine (BCP) buffer layer, and copper (Cu) metal contact.

“Two rectangular shapes with 1 cm 2 active area have been designed, with the aim to reduce resistive losses occurring mostly at the TCO electrode: the active areas are defined by a P3 scribe, followed by a P2 scribe to use the remaining metal electrode as a current collecting electrode for the TCO,” the researchers said, noting that using the P2-P3 process enabled the integration of a current collecting grid using the same metal layer as the top electrodes.

The group tested a module built with this architecture and an ultranarrow interconnection of 19.5 μm under standard illumination conditions and found it can reach an efficiency of 20.7%, a fill factor of 81.7%, and a geometrical fill factor of 96%, with no relevant resistive losses being detected.

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Looking forward, the team said it wants to apply an unspecified advanced alignment procedure to avoid possible warping of the module during processing. “By applying this novel approach to the semitransparent modules made in Solertix, we are close to achieving a 30% efficiency using an area-matched 4T tandem with a perovskite module over a silicon cell,” Di Giacomo said, without providing further details.

Solartix was acquired by FuturaSun in June 2023. It was created at the Organic Solar Center (CHOSE), which was set up by Professor Aldo Di Carlo, who also assumed the position of president of the scientific committee of the Italian startup.

In March 2021, the University of Rome Tor Vergata presented a perovskite solar module with a total active area of 42.8 cm2 and aperture area of 50 cm2. The panel was built with 20%-efficient perovskite cells connected in 14 series and was able to retain 90% of the initial efficiency after 800 h of thermal stress at 85 degrees Celsius.

A few months later, it unveiled a perovskite solar module with cells based on triple-cation cesium methylammonium formamidinium (CsMAFA).

 

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