Prof. Man-Jong Lee Develops Perovskite Solar Cells Without Dry Room Installation
Professor Man-Jong Lee from College of Sciences (Department of Chemistry) at Konkuk University announced on the 27th that his research team has developed a new way of producing a next-generation perovskite solar cells even in wet conditions. (Thesis title: Ambient-air fabrication of stable mixed cation perovskite planar solar cells with efficiencies exceeding 22% using a synergistic mixed antisolvent with complementary properties)

The research result was published on July 20th in ‘Nano Energy’, the international journal in the field of energy and materials.

The fact that perovskites should be manufactured in a strict environment has been a major risk factor in terms of facility investment cost. The result increased the possibility of commercialization showing that solar cells can be manufactured without dry rooms or nitrogen glove boxes with high facility investment cost.

Perovskite solar cells use perovskite substances instead of silicon as light absorbing layer. Although it has an advantage of high efficiency and being able to manufacture with a relatively simple solution method, manufacturing facilities and the like remain an unsettled problem of commercialization. As precursor solution combines with moisture at high humidity and disturbs the formation of high-quality perovskite crystals, a dry room with low humidity had to be installed.

A research team of Prof. Lee developed a new method of anti-solvent cleaning that can produce high efficiency perovskite solar cells in general wet atmospheric condition (relative humidity > 40%).

In order to offset the effect of humidity, the research team developed a process of removing solvents with a mixture of dibutyl ether and diethyl ether, which have complementary low vapor pressure and low boiling point.

The perovskite solar cells made by the research team reached the highest efficiency of 22.06% among perovskite solar cells made in wet atmospheric conditions maintaining 94% of the initial efficiency after 1200 hours, thus proving its safety.

Prof. Lee said, “We have suggested that high efficiency perovskite solar cells can be manufactured in wet conditions getting over from strictly controlled environment,” adding that, “It is expected to contribute to the commercialization of perovskite solar cells.”

Major Research Findings 1. Needs of Research
  • - The organic-inorganic cation mixed perovskite solar cells are being highlighted as a next-generation solar cell with an efficiency of 25.5% in a short period of time, and global research is being focused on carbon neutrality and green energy.
  • - The organic ingredients, however, are extremely vulnerable to moisture, high efficiency perovskite solar cells can only be manufactured in strict conditions where moisture and oxygen have been completely removed.
  • - Such a strict manufacturing environment can be an obstacle in the widespread commercialization and dissemination of high efficiency perovskite solar cells as it determines facility investment cost
  • - Therefore, it is necessary to develop a method of manufacturing high efficiency perovskite solar cells that work stably under general wet conditions.
  • - To this end, it is essential to select an anti-solvent that limits moisture contact during the washing process and simultaneously enables the defect-free particle growth of the photoactive layer.
● anti-solvent: ● anti-solvent washing:
2. Needs of Research
  • - Volatile materials such as diethyl ether and chlorobenzene, which are advantageous in controlling the growth of perovskite, are actively used during the anti-solvent washing process.
  • - However, it becomes a problem as perovskite cannot be protected from moisture in the atmosphere during the process of forming an active layer of perovskite considering that the existing anti-solvent evaporates fast in wet conditions (relative humidity of 40% or more). Organic matter bonded to moisture combined with moisture cause fatal defects such as deformation or stress of the perovskite layers resulting in adverse effects in solar cell efficiency.
  • - The research team developed high efficiency perovskite solar cells with no deformation or stress even under wet conditions by using dibutyl ether/diethyl ether mixed solvent with complementary features in the anti-solvent washing method.
  • - Dibutyl ether, an ether solvent, is easy to mix with others and has low vapor pressure. Thus, the washing method using a mixed anti-solvent may minimize bonding of the organic matter of the perovskite precursor with moisture during 1-step coating. Diethyl ether led the growth of perovskite active layers by removing residual solvents from an effective perovskite precursor solution. That is, an element with high efficiency and long-term stability was developed through the synergy effect of the mixed anti-solvent.
  • - As a result, the research team succeeded in manufacturing perovskite solar cells with high efficiency of 22.06% under wet conditions. The team also confirmed that more than 94% of initial performance was maintained after 1200 hours when the manufactured solar cells were continuously exposed to wet conditions.
  • - These characteristics were further identified through simulation using a supercomputer (DFT), strain analysis and charge mobility measurement.
3. Expected Outcome
  • - The research team developed perovskite solar cells with the world’s highest efficiency and stability of 22.06% under wet conditions. It is expected to contribute to the commercialization of perovskite solar cells by providing clues to improve the active layers under wet conditions.

    (Image 1) A schematic diagram of perovskite production process using anti-solvent washing method

    The research team used anti-solvent washing method to obtain perovskite crystals, and synthesized perovskite thin film by varying the anti-solvent washing solvent under wet conditions. In case of using diethyl ether as single solvent (image above), the perovskite thin film could be deformed, however, dibutyl ether/diethyl ether mixed solvent (image below) could manufacture a high-quality perovskite thin film in which the defect was removed and not deformed.

    (Image 2) Efficiency and stability of perovskite solar cells made in wet conditions

    (Left) After simulating (DTF) each structure obtained while using diethy ether and dibutyl ether/diethyl ether mixed anti-solvent, it was confirmed that the structure was deformed when a perovskite organic matter was combined with water
    (Center) Efficiency (J-V) of 22.06% (based on the cell area of 0.10 cm2) of perovskite solar cells obtained from mixed anti-solvent processing
  • - (Right) More than 94% of initial performance was maintained after 1200 hours when the manufactured solar cells were continuously exposed to wet conditions.

    Images provided and explained by Prof. Man-Jong Lee at Konkuk University