Tag Archives: hydrophobic conducting polymer

Making perovskite solar cells more stable and more humidity tolerant

Living in what’s considered a humid environment the news of solar cells that are humidity-resistant caught my attention. From a July 18, 2016 news item on phys.org,

Widely known as one of the cleanest and most renewable energy sources, solar energy is a fast growing alternative to fossil fuels. Among the various types of solar materials, organometal halide perovskite in particular has attracted researchers’ attention thanks to its superior optical and electronic properties. With a dramatic increase in the power conversion efficiency (PCE) from 3% in 2009 to as high as over 22% today [according to my July 13, 2016 posting that efficiency could now be as high as 31%], perovskite solar cells are considered as a promising next-generation energy device; only except that perovskite is weak to water and quickly loses its stability and performance in a damp, humid environment.

A team of Korean researchers led by Taiho Park at Pohang University of Science and Technology (POSTECH), Korea, has found a new method to improve not only the efficiency, but stability and humidity tolerance of perovskite solar cells. Park and his students, Guan-Woo Kim and Gyeongho Kang, designed a hydrophobic conducting polymer that has high hole mobility without the need of additives, which tend to easily absorb moisture in the air. …

A July 18, 2016 Pohang University of Science and Technology (POSTECH) press release on EurekAlert, which originated the news item, provides more information about the work,

Perovskite solar cells in general consist of a transparent electrode, an electron transport layer, perovskite, a hole transport layer, and a metal electrode. The hole transport layer is important because it not only transports holes to the electrode but also prevents perovskite from being directly exposed to air. Spiro-MeOTAD, a conventionally used hole-transport material, needs additives due to its intrinsically low hole mobility. However, Bis(trifluoromethane)sulfonimide lithium salt (LiTFSI), one of the common additives, is prone to suck in moisture in the air. Moreover, Spiro-MeOTAD forms a slightly hydrophilic layer that easily dissolves in water, and thus it cannot work as a moisture barrier itself.

Park’s team focused on an idea of an additive-free (dopant-free) polymeric hole transport layer. They designed and synthesized a hydrophobic conducting polymer by combining benzodithiophene (BDT) and benzothiadiazole (BT). As the new polymer has a face-on orientation, which helps vertical charge transport of holes, the researchers were able to achieve high hole mobility without any additives.

Park and colleagues confirmed that the perovskite solar cells with the new polymer showed high efficiency of 17.3% and dramatically improved stability — the cells retained the high efficiency for over 1400 hours, almost two months, under 75 percent humidity.

“We believe that our findings will bring perovskite one step closer to use and accelerate the commercialization of perovskite solar cells,” commented Taiho Park, a professor with the Department of Chemical Engineering at POSTECH.

Here’s a link to and a citation for the paper,

Dopant-free polymeric hole transport materials for highly efficient and stable perovskite solar cells by Guan-Woo Kim, Gyeongho Kang, Jinseck Kim, Gang-Young Lee, Hong Il Kim, Limok Pyeon, Jaechol Lee, and Taiho Park. Energy Environ. Sci., 2016,9, 2326-2333 DOI: 10.1039/C6EE00709K First published online 28 Apr 2016

I wonder if the press release was originally written in April 2016? That would explain the difference in efficiency I noted earlier in the press release. Getting back to the paper, it is open access with three different means of accessing the material from the publisher, the Royal Society of Chemistry.