[Research Necessity]

Solar power generation is a key renewable energy source for reducing carbon emissions and building a sustainable energy system. Among these, perovskite thin-film solar cells are gaining prominence as a next-generation technology, based on their advantages of being lightweight and flexible, having outstanding power conversion efficiency, and a low-cost manufacturing process.

However, performance degradation due to defects and a lack of long-term stability are still pointed out as the most significant challenges hindering commercialization. Especially, various defects that form during the crystallization process and device operation are concentrated at the surface and grain boundaries of the thin film, causing charge recombination and shortening the device's lifespan. These defects act as nonradiative recombination centers and can also become pathways for ion migration, leading to material decomposition or phase segregation.

Specifically, lead (Pb)-based deep-level defects are identified as a primary cause that shortens the cell's lifespan and significantly degrades its stability. Accordingly, technology to effectively control and passivate these defects is urgently needed.

 

[Research Objective]

This study aims to introduce the concept of chelation to effectively passivate lead (Pb) defects within perovskite solar cells. The goal is to simultaneously achieve a reduction in defect density, an improvement in charge transport properties, the suppression of non-radiative recombination, and the attainment of long-term stability.

 

[Research Content]

Chelation is a method where a single molecule forms multiple bonds with a metal ion through several functional groups, providing higher stability than a single bond. The research team selected candidate materials from naturally derived chelating agents and conducted a comparative analysis of their interaction strength with lead ions based on their structure and the number of functional groups.

As a result, it was confirmed that citric acid, which has three carboxyl groups (-COOH) and one hydroxyl group (-OH), forms the strongest bond with lead ions.

By applying citric acid to the perovskite thin film, the team effectively reduced the density of defects at the grain boundaries and surface, suppressing charge recombination losses.

 

[Research Results]

The citric acid treatment led to an improved open-circuit voltage.

The power conversion efficiency (PCE) increased from 20.7% to 22.0%.

Even without an encapsulation process, the device maintained over 90% of its initial efficiency during 150 hours of continuous operation in the air.

→ Demonstrates that excellent long-term stability was secured.

 

[Significance and Impact]

Utilizing an eco-friendly and inexpensive natural material like citric acid as a defect control agent is a highly original approach.

This work not only improved efficiency but also realized a level of durability that allows for stable, long-term operation without additional protection.

It presents a practical solution to the chronic problem of perovskite solar cells: the lack of long-term stability.

The proposed chelation-based defect control strategy has high potential for application beyond solar cells.

→ It can be extended to various perovskite-based optoelectronic devices, such as photosensors and light-emitting devices. This work is evaluated as a core technology that can accelerate the commercialization of next-generation solar cells and contribute to realizing a carbon-neutral society and the popularization of renewable energy technology.

 

[Achievements and Publication Information]

This research was published in the international journal Solar RRL and was selected as a front cover article in recognition of its excellence.