A research team led by Professor Noh Jun Hong has published an article in Nature, one of the world’s most popular scientific journals

Introduced as a next-generation halide perovskite solar cell technology that can open the door to commercialization

Expected to ramp up technological development to commercialize perovskite solar cells

▲ Professor Noh Jun Hong from the Department of Civil, 

Environmental and Architectural Engineering in the College of Engineering

Professor Noh Jun Hong from the Department of Civil, Environmental and Architectural Engineering in the College of Engineering published a research paper on ‘next-generation halide perovskite solar cell technology that can open the door to commercialization in the March 27, 2019 edition of Nature (IF = 41.577).

- Title: Efficient, stable and scalable perovskite solar cells using poly (3-hexylthiophene)

- Author information: Jung Eui Hyuk (first author of the study, postdoctoral researcher at the Korea Research Institute of Chemical Technology), Noh Jun Hong (co-corresponding author, Associate Professor at the Department of Civil, Environmental and Architectural Engineering of the College of Engineering, Korea University and Associate Researcher at the Korea Research Institute of Chemical Technology), Seo Jangwon (Co-corresponding author, Principal Investigator at the Korea Research Institute of Chemical Technology)

Professor Noh, a co-corresponding author of the study, has worked on perovskite solar cells in collaboration with researchers from the Korea Research Institute of Chemical Technology. "We succeeded in maximizing the performance of highly durable conductive commercial polymers by realizing a double-layered halide architecture (DHA) as a solution process," he said.

The research applied a technology close to commercialization and found a breakthrough that can achieve high efficiency, high stability, and large-area modulation simultaneously. Perovskite solar cells have been receiving attention as a next-generation solar cell because they are cheap and easy to manufacture. The 'Renewable Energy 3020 Action Plan' announced recently by the Korean government has named the cells as a next-generation technology to replace silicon solar cells. The DHA has a wide band-gap halide (WBH) layer stacked onto a narrow band-gap halide (NBH) light-absorbing layer developed in this study (*See figures).

There are several obstacles to the commercialization of perovskite solar cells. Existing hole-transport materials (HTMs) are expensive and require dopants to ensure high conductivity, which, however, weakens the stability of the solar cells. Also, mass production of uniform materials is needed for large-area print coatings, which cannot be fully addressed with the conventional hole-transport materials.

* The most common hole-transport materials are PTAA and Spiro-OMeTAD polymers. Holes carry current to particles with a positive charge.

* In general, a small amount of hydrophilic additives (Li-TFSI, tert-butyl pyridine, etc.) are doped.

Conductive commercial polymer P3HT is an alternative hole-transport material that meets all these requirements. Since it has already been used for organic solar cells and organic transistors, attempts have been made to use it for perovskite solar cells, but its low power conversion efficiency of 16% has remained a problem.

* P3HT: Poly (3-hexylthiophene), a polymer hole-transport material

To solve this problem, the researchers fabricated the DHA by depositing a new thin solution-processed film of halide with a wide-bandgap on the surface of the light-absorbing perovskite halide thin film. In fabricating the DHA, the HTAB molecules with the same alkyl chain as the P3HT were used to make the alkyl chains of HTAB and P3HT coupled with each other like a zipper. This induced self-assembly of the hole-transporting layer P3HT and thereby maximized the hole-transfer and -transport effects.

* Alkyl chain: a part of a molecule that consists of carbons and hydrogens in chains.

* HTAB: Hexyl Trimethyl Ammonium Bromide molecule

Existing HTMs require the use of hydrophilic additives to enhance the hole-transporting capacity. This study, however, attained high durability without any additive using the maximized hole transfer and transport performance of the self-assembled P3HT polymer.

When stored for over 1,000 hours at relative humidity of 85%, the perovskite solar cell developed in this study maintained 80% of its initial efficiency. The vulnerability of perovskite to moisture was an obstacle to its commercialization, but the DHA-based perovskite solar cells showed high moisture stability.

maintained 95% or more of its initial efficiency when used for over 1,300 hours under actual-use conditions, proving its long-term operational stability. This high moisture stability and long-term operational stability suggests that high efficiency can be maintained for a long period even in an outdoor environment where the solar cell is actually used.

The study also showed the potential for large-area modulation, a prerequisite for commercialization. The research team extended the technology confirmed in the 0.1 cm2 unit device to a large-area module of 25cm2 and achieved a certified high efficiency of 16% at the large-area module of 25cm2.

Professor Noh said, "Perovskite solar cells have already been recognized in terms of efficiency and stability, but what technology can be used to realize them is the key to commercialization. This work has significant implications in that that it is not an improvement of the existing technology in terms of efficiency and durability, but the development of a breakthrough technology closer to commercialization.”

The A co-corresponding author of the study, Dr. Jangwon Seo of the Korea Research Institute of Chemical Technology said, "As we have succeeded in developing a new concept perovskite thin film technology that ensures high efficiency and high stability of perovskite solar cells using conductive commercial polymers, a variety of conductive polymers are expected to be used broadly, which will also contribute to performance enhancements of the perovskite solar cell devices. As it is possible to develop high-efficiency large-area modules through an optimized process, we are even closer to commercialization now."

[Description of figures]

(Top) Schematic diagram of the DHA-based device and self-assembly concept drawing of P3HT

(Bottom left) Surface of general amorphous P3HT film and of P3HT self-assembled by the DHA

(Bottom right) Enhanced performance of the DHA / P3HT solar cells and current density-voltage curves