Wednesday, 22 May 2019

Researchers make progress in solving a major challenge in mass production of perovskite solar cells

Spray coating could make perovskite an inexpensive alternative to silicon for solar panels

NYU Tandon - A model of a perovskite solar cell showing its different layers-

15 Jun 2018 | Editor

An international team of university researchers have reported solving a fabrication challenge for perovskite solar cells.

In the published paper the research team reveals a new scalable means of applying a critical component to perovskite cells to solve some major fabrication challenges. The researchers were able to apply the critical electron transport layer (ETL) in perovskite photovoltaic cells in a new way - spray coating - to imbue the ETL with superior conductivity and a strong interface with its neighbour, the perovskite layer.

The research was led by Andre D. Taylor, an associate professor in the NYU Tandon School of Engineering’s Chemical and Biomolecular Engineering Department, with Yifan Zheng, the first author on the paper and a Peking University researcher. Co-authors are from the University of Electronic Science and Technology of China, Yale University, and Johns Hopkins University.

According to the researchers most solar cells are "sandwiches" of materials layered in such a way that when light hits the cell's surface, it excites electrons in negatively charged material and sets up an electric current by moving the electrons toward a latticework of positively charged "holes."

In perovskite solar cells with a simple planar orientation called p-i-n (or n-i-p when inverted), the perovskite constitutes the light-trapping intrinsic layer (the "i" in p-i-n) between the negatively charged ETL and a positively charged hole transport layer (HTL).

When the positively and negatively charged layers are separated, the photons from a light source dislodge unstable electrons from the ETL, causing them to fall toward the positive HTL side of the sandwich. The perovskite layer expedites this flow. While perovskite makes for an ideal intrinsic layer because of its strong affinity both for holes and electrons and its quick reaction time, commercial-scale fabrication has proved challenging partly because it is difficult to effectively apply a uniform ETL layer over the crystalline surface of the perovskite.

The researchers chose the compound [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) because of its track record as an ETL material and because PCBM applied in a rough layer offers the possibility of improved conductivity, less-penetrable interface contact, and enhanced light trapping.

The most common method is spin casting, which involves spinning the cell and allowing centripetal force to disperse the ETL fluid over the perovskite substrate. But this technique is limited to small surfaces and results in an inconsistent layer that lowers the performance of the solar cell. Spin casting is also inimicable to commercial production of large solar panels by such methods as roll-to-roll manufacture, for which the flexible p-i-n planar perovskite architecture is otherwise well suited.

The researchers instead turned to spray coating, which applies the ETL uniformly across a large area and is suitable for manufacturing large solar panels. They reported a 30 percent efficiency gain over other ETLs - from a PCE of 13 percent to over 17 percent - and fewer defects.

The Foundation of the National Natural Science Foundation of China (NSFC), the Foundation for Innovation Research Groups of the NSFC, the Chinese Scholarship Council, and the U.S. National Science Foundation provided funding for the study.

"Very little research has been done on ETL options for the planar p-i-n design."

"The key challenge in planar cells is, how do you actually assemble them in a way that doesn’t destroy the adjacent layers?"

"Our approach is concise, highly reproducible, and scalable. It suggests that spray coating the PCBM ETL could have broad appeal toward improving the efficiency baseline of perovskite solar cells and providing an ideal platform for record-breaking p-i-n perovskite solar cells in the near future."

Andre D. Taylor, Associate professor in the NYU Tandon School of Engineering

Spray coating of the PCBM electron transport layer significantly improves the efficiency of p-i-n planar perovskite solar cells

Yifan Zheng | Jaemin Kong | Di Huang | Wei Shi | Lyndsey McMillon-Brown | Howard E. Katz | Junsheng Yu | Andre D. Taylor


The p-i-n structure for perovskite solar cells has recently shown significant advantages in minimal hysteresis effects, and scalable manufacturing potential using low-temperature solution processing. However, the power conversion efficiency (PCE) of the perovskite p-i-n structure remains low mainly due to limitations using a flat electron transport layer (ETL). In this work, we demonstrate a new approach using spray coating to fabricate the [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) ETL. By creating a rough surface, we effectively improve the light trapping properties inside the PCBM ETL. We reveal that the spray coated PCBM can form a cross-linked network, which may facilitate better charge transport and enhance extraction efficiency. By improving the contact between the perovskite film and the PCBM ETL, a reduction in the trap states is observed resulting in a PCE increase from 13% to >17%.


About NYU Tandon

The NYU Tandon School of Engineering dates to 1854, the founding date for both the New York University School of Civil Engineering and Architecture and the Brooklyn Collegiate and Polytechnic Institute (widely known as Brooklyn Poly). A January 2014 merger created a comprehensive school of education and research in engineering and applied sciences, rooted in a tradition of invention and entrepreneurship and dedicated to furthering technology in service to society. In addition to its main location in Brooklyn, NYU Tandon collaborates with other schools within NYU, one of the country’s foremost private research universities, and is closely connected to engineering programs at NYU Abu Dhabi and NYU Shanghai. It operates Future Labs focused on start-up businesses in downtown Manhattan and Brooklyn and an award-winning online graduate program.

Source: NYU Tandon

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