Perovskite solar cells achieve over 25% efficiency and long lifespan simultaneously

A KAIST research team has solved the "solar cell dilemma," in which increasing efficiency shortens lifespan, while extending lifespan lowers efficiency. The team developed a technology to precisely control the internal structure of a surface passivation layer in perovskite solar cells, successfully achieving both high efficiency exceeding 25% and long-term stability at the same time. The study is published in the journal Joule.

New design for perovskite passivation

A research team led by Distinguished Professor Jangwon Seo of the Department of Chemical and Biomolecular Engineering, in joint research with the Korea Research Institute of Chemical Technology (KRICT), developed a 2D passivation layer design technology that simultaneously improves the efficiency and long-term stability of perovskite solar cells.

As the need to respond to the climate crisis and transition energy systems grows, improving the efficiency of solar power generation and securing long-term reliability have emerged as important challenges.

In particular, perovskite solar cells, which are attracting attention as next-generation high-efficiency solar cells, have recently achieved rapid efficiency improvements. However, they have been pointed out as having commercialization barriers due to performance degradation under high temperature, high humidity, or prolonged light exposure.

Previously, a 3D/2D structure strategy—adding a 2D layer on top of a 3D perovskite layer—has been used. This method helps reduce surface defects and improve stability. However, if the structure of the 2D layer is not sufficiently robust, it has limitations in that the structure may deform over time or performance may gradually decline.

How the DJ structure solves instability

To address this, the research team introduced a structurally more stable Dion–Jacobson (DJ) type 2D perovskite passivation layer and proposed a design strategy that precisely controls the "n value," which refers to the number of stacked perovskite layers within the passivation layer.

The DJ structure enhances structural stability by firmly connecting perovskite layers with organic molecules on both sides. In simple terms, it is similar to binding bricks together with a stronger adhesive so that the structure does not easily collapse.

The research team controlled the stacking structure (n value) of perovskite layers inside the 2D passivation layer in a desired manner by adjusting heat treatment conditions, analogous to how controlling temperature and time during the curing of adhesive after stacking bricks results in a more solid and orderly structure.

Proven gains in efficiency and durability

As a result, charge transport became more efficient, improving solar cell efficiency, and the robust characteristics of the DJ structure also enhanced long-term stability.

In addition, the team experimentally revealed that during the heat treatment process, the internal structure of the 2D passivation layer changes as the structure is rearranged at the interface where different materials meet. They also presented the principles for controlling the passivation layer structure and reproducible process conditions.

The perovskite solar cell applying this design strategy recorded a high power conversion efficiency of 25.56% (certified efficiency of 25.59%). It also maintained a high level of performance under conditions of 85°C and 85% relative humidity (85% RH) as well as continuous light exposure, confirming long-term stability.

The research team further applied this technology to the fabrication of large-area modules and verified excellent performance.

Distinguished Professor Jangwon Seo stated, "This study demonstrates that the longstanding challenge—where increasing efficiency reduces lifespan and increasing lifespan lowers efficiency—can be solved simultaneously through structural design of the surface passivation layer. This technology operates relatively stably even under changes in process conditions, making it helpful for large-area manufacturing processes for commercialization."

Provided by The Korea Advanced Institute of Science and Technology (KAIST)