Translucent tandem perovskite-perovskite solar cells for BIPV

A group of scientists led by Germany's Karlsruhe Institute of Technology (KIT) has developed a new way to fabricate micro-patterned translucent perovskite PV cells that could be used in tandem solar modules intended for applications in building-integrated photovoltaics (BIPV).

“While translucent perovskite multi-junction devices have been envisaged and recognized as a promising path towards high- efficiency neutral-color transparent PV, the tolerance of complex perovskite tandem stacks against extensive laser scribing has yet to be explored,” the research group said.

The researchers noted that the cells have thus far provided decent levels of power conversion efficiency while maintaining a high average visible transmittance (AVT). They used a custom-built laser scribing setup to fabricate a perovskite solar cell with n–i–p architecture and with an active area of 0.105 cm 2. The device is based on an indium tin oxide (ITO) substrate, a hole transport layer made of carbazole (2PACz), an electron transport layer made of buckminsterfullerene (C60), an absorber based on methylammonium lead triiodide (CH3NH3PbI3), a bathocuproine (BCP) buffer layer, and a gold (Au) metal contact.

They scaled up the cell area by a factor of 40 to 4 cm2 to reach an AVT of 30%. They combined four of these cells into a mini module with an area of 20 mm x 4 mm.

“The monolithic series interconnections are fabricated via laser scribing of the established P1–P2–P3 lines,” they explained.

The mini panel has an efficiency of 9.0% at 32% AVT, an open-circuit voltage of 5.5 V, a short-circuit current density of 11.1 mA cm2, and a fill factor of 74%.

The group also built a two-terminal (2T) tandem perovskite-perovskite solar cell that reached a power conversion efficiency of up to 17.7% at 12% AVT. It also achieved an open-circuit voltage of 1.95 V, a short-circuit current of 11.9 mA cm2, and a fill factor of 77%.

“Following subsequent upscaling, a translucent tandem mini-module with 12.25 cm 2 aperture area, similar device architecture and fabricated via fully scalable deposition methods provides promising 10.3% efficiency at 15% AVT while further optimizations,” they said.

The group claims that the cells are the best-performing translucent perovskite tandem solar cells fabricated at the research level to date.

“The devices successfully demonstrate the good electrical performance as well as uniform optical impression of the implemented transmittance gradients, being enabled by the versatile laser scribed translucent photovoltaics,” they said.

They described the cell technology in “Translucent perovskite photovoltaics for building integration,” which was recently published in Royal Society of Chemistry.