Improving perovskite solar cell performance with conductive adhesive ink

A group of scientists led by the Sharif University of Technology in Iran developed a new conductive adhesive ink that can be used as an interfacial adhesive layer in perovskite solar cells.

“The adhesive ink is intended to improve the cell stability and efficiency,” the research's corresponding author, Nima Taghavinia, told pv magazine. “We developed a low-cost and simple process that is compatible with large-area applications.”

The adhesive is made of polymethyl methacrylate (PMMA), which is a widely used polymer as a substitute for glass in various industries based on its low cost, excellent mechanical, electrical, and optical properties, thermal and environmental stability, low weight, and high light transparency. It is utilized as interfacial layer between the cell's hole transport layer (HTL) made of copper indium sulfide (CuInS2) nanoparticles and a top carbon foil relying on highly conductive carbon black (HCCB).

The adhesive was embedded in a cell consisting of a substrate made of fluorine-doped tin oxide (FTO), an electron transport layer (ETL) based on carbon–titanium dioxide (c/TiO2), a TiO2 mesoporous layer, the perovskite absorber, the HTL based on CuInS2, and the top carbon foil with HCCB.

The researchers noted that this cell configuration without the new adhesive had previously proved to be unstable, as the carbon electrodes were frequently detached after taking measurements.

“The conductive adhesive ink was drop-casted onto the carbon foil with area of 0.27 cm2,” the researchers said, referring to the adhesive deposition process. “The carbon foil was then transferred onto the as-prepared FTO glass/c-TiO2/mp- TiO2/perovskite/CuInS2 stack in a way that the adhesive ink is in contact with the HTL.”

Through a series of tests, the research group found that the PMMA is the key for achieving stable and reliable adhesion of carbon foil to the cell. It also explained that adding the CuInS2 nanoparticles to the ink makes the adhesive consistent with the underlying HTL, with the CuInS2 nanoparticles contributing to the hole transfer mechanism.

“Our results showed that adding 2 %wt of HCCB nanoparticles to the PMMA/CIS mixture with a ratio of 1:3 leads to the maximum conductivity for the achieved adhesive interfacial layer, resulting in the maximum efficiency of 17.2 %, which is comparable with that of gold-based counterpart cells (18.2 %),” the academics stated. “Moreover, utilizing the proposed carbon-laminated electrode we achieved a long-term stability of about 92 % after 54 days of storage, which is about 17 % enhancement in comparison with the stability of gold-based counterparts.”

Their findings are available in the study “A conductive adhesive ink for carbon-laminated perovskite solar cells with enhanced stability and high efficiency,” published in Solar Energy.