Lighter and more flexible solar cells achieve world’s highest efficiency
KIER achieves world’s highest efficiency of 23.64% with flexible perovskite/CIGS thin-film tandem solar cell
National Research Council of Science & Technology
image:
Group photo of the research team (from left Professor Hae-Jin Kim from Yonsei University, Dr. Inyoung Jeong from KIER, Dr. Kihwan Kim, and Professor Tae Kyung Lee from Gyeongsang National University)
view moreCredit: KOREA INSTITUTE OF ENERGY RESEARCH(KIER)
The Korea Institute of Energy Research (President Yi Chang-keun, hereinafter referred to as “KIER”) has successfully developed ultra-lightweight flexible perovskite/CIGS tandem solar cells and achieved a power conversion efficiency of 23.64%, which is the world’s highest efficiency of the flexible perovskite/CIGS tandem solar cells reported to date. The solar cells developed by the research team are extremely lightweight and can be attached to curved surfaces, making it a promising candidate for future applications in buildings, vehicles, aircraft, and more.
Crystalline silicon-based single-junction solar cells are predominantly used in solar power generation due to their low production cost and suitability for mass manufacturing. However, as the efficiency of single-junction solar cells approaches their theoretical limit, tandem solar cells— which combine silicon with perovskite* solar cells to enhance efficiency—are gaining increasing attention.
* Perovskite: A material with a crystal structure similar to calcium titanate (CaTiO₃), known for its excellent light absorption properties, making it a promising next-generation solar cell material.
Currently, perovskite/silicon tandem solar cells have achieved efficiencies as high as 34.6%. However, their heavy weight and susceptibility to physical damage limit their application in fields where lightness and adaptability are critical, such as in automobiles, aircraft, and satellites.
To overcome these limitations, flexible thin-film perovskite/CIGS* tandem solar cells are being developed. CIGS-based thin-film solar cells are extremely lightweight and flexible, making them well-suited for use on curved surfaces such as buildings, vehicles, and aircraft. However, their lower efficiency and greater manufacturing complexity compared to perovskite/silicon tandem solar cells have posed barriers to commercialization
A cross-sectional image of a perovskiteCIGS tandem solar cell taken with an electron microscope
Credit
KOREA INSTITUTE OF ENERGY RESEARCH(KIER)
*CIGS: A compound semiconductor made of copper, indium, gallium, and selenium (CuIn₁₋ₓ GaₓSe₂), known for its excellent photoelectric properties. It is used as a light-absorbing layer in thin-film solar cells. In particular, it can be fabricated on highly flexible substrates such as polyimide or metal films, giving it exceptional flexibility.
To enhance the manufacturability, flexibility, and lightness of tandem solar cells, the KIER research team developed a simple lift-off process and identified the underlying mechanisms behind the performance improvement. As a result, the fabricated perovskite/CIGS tandem solar cell achieved a power conversion efficiency of 23.64%, representing the highest recorded efficiency among flexible perovskite/CIGS tandem solar cells reported to date.
The lift-off process developed by the research team involves coating a polyimide layer onto a glass substrate, fabricating the perovskite/CIGS tandem solar cell on top of it, and then separating it from the glass. Unlike conventional methods that use flexible polyimide film directly as the substrate, this approach utilizes rigid glass as a supporting base, allowing for more stable fabrication of the solar cells. The use of a flat, rigid glass substrate also ensures uniform layer deposition, leading to improved device performance and higher reproducibility.
The research team also identified a method to enhance performance by reducing defects in the solar cell. During the fabrication process, alkali metal elements such as potassium diffuse from the glass substrate into the CIGS light-absorbing layer. Excessive diffusion of potassium can create defects within the absorber layer that hinder charge transport, ultimately degrading the performances of the solar cells. However, until now, no technology had been reported that effectively suppresses the diffusion of potassium to an optimal level.
Using computational science, the research team predicted that the polyimide layer coated on the glass substrate could suppress potassium diffusion. When applied to the solar cell fabrication process, this approach effectively reduced defects in the CIGS light-absorbing layer. As a result, the fabricated device achieved a power conversion efficiency of 23.64%, significantly exceeding the previous record of 18.1% for flexible perovskite/CIGS tandem solar cells.
In addition, to verify the durability of the fabricated CIGS solar cells, the research team measured the mechanical properties of the materials and analyzed the stress applied during bending through simulations. After conducting 100,000 bending cycles, the solar cells maintained 97.7% of their initial efficiency, demonstrating excellent durability.
Dr. Inyoung Jeong, who led the study, stated, “This research is a key achievement that demonstrates the commercial potential of next-generation high-efficiency solar cell technology with flexibility and lightness,” adding, “It serves as an important milestone toward realizing ultralight, flexible solar cells with 30% efficiency in the future.”
Dr. Kihwan Kim, principal investigator of the study, stated, “The power-to-weight ratio of the fabricated solar cell is approximately 10 times higher than that of perovskite/silicon tandem solar cells, making it highly promising for applications in fields that require ultralight solar modules, such as building exteriors, vehicles, and aerospace.” He added, “By advancing large-area fabrication processes and improving stability, we aim to strengthen the competitiveness of related industries and significantly contribute to the expansion of renewable energy adoption.”
Meanwhile, this research was published in the March issue of Joule (Impact Factor: 38.6), a prestigious international journal in the field of energy and materials. The study was conducted with support from the Research and Development Program of the Korea Institute of Energy Research, in collaboration with Professor Tae Kyung Lee of Gyeongsang National University and Professor Hae-Jin Kim of Yonsei University.
Journal
Joule
Article Title
Flexible and lightweight perovskite/Cu(In,Ga)Se2 tandem solar cells
Launch of the “PV Doctor” - the future of solar PV asset performance management
Launch of the “PV Doctor” – we listen, we analyze, we cure
The "PV Doctor", launched on 2 April 2025, is a spin-off from the Solar Energy Research Institute of Singapore (SERIS) at the National University of Singapore (NUS). It commercialises 15 years of in-depth research on PV system performance in different climates and on maximising energy yield – be it for well-operating (“healthy”) or under-performing (“sick”) installations.
The "PV Doctor" offers a unique combination of cutting-edge data analytics using artificial Intelligence (AI), daily routine checks and performance benchmarks. This ensures that PV assets under management (AUM) operate at optimum yield at any time.
Beyond the data-driven part, the “PV Doctor” also offers to rectify under-performing PV assets and bring them back to optimum energy yield levels. This will ensure higher revenues and ultimately higher returns on investment for PV system owners. The “PV Doctor” was founded with a clear mission: to ensure that every signed-up PV system operates at its peak performance, delivering the value that owners expect.
By combining cutting-edge AI-driven analytics with decade-long expertise in PV system behaviour, we provide real-time monitoring, alarm conditioning and actionable solutions that prevent energy losses and protect long-term asset value.
Background
Solar PV systems are often sold under the assumption of “zero maintenance”. While the maintenance efforts for PV installations compared to other energy generating technologies with moving parts are much lower, they are not “zero” at all. In fact, a recent study shows that – globally – the annual amount of preventable losses of operating PV assets is USD 10 billion! Obviously, there are many “sick” patients out there. And that’s where the “PV Doctor” comes into the picture and helps owners of under-performing assets to find out the underlying root causes and rectifies them until the system is back to expected energy yields. Likewise, the “PV Doctor” also monitors “healthy” PV systems
using its proprietary “Smart O&M” algorithm to make sure that the assets don’t move into “unhealthy” performance ranges in the first place.
Fast ramp-up
The “Smart O&M” services were initially offered through SERIS to clients across Asia – and the sign-up rates prove the enormous demand in the region. In less than 12 months, the assets under management (AUM) climbed to over 200 MWp, across 400 sites in 10 countries. In Singapore alone, more than 3% of all PV installations are already under “Smart O&M” monitoring by the “PV Doctor”. The new spin-off brings these numbers to new heights and also offers a much broader service base.
Comprehensive List of Service Offerings by the “PV Doctor”
The “PV Doctor” is a one-stop shop for both well-operating and under-performing PV installations – irrespective of the system size. We work with all types of clients (such as system owners, developers, EPCs, O&M companies) and all system sizes from small residential to C&I installations and utility-scale solar farms.
Below is a list of the six core services that the “PV Doctor” offers to clients:
1. Smart O&M – Keeping systems at best performance levels through real-time monitoring
The core of “PV Doctor’s” services is Smart Operations & Maintenance (“Smart O&M”), a data-driven solution that automatically detects performance issues, analyses root causes, and proposes corrective actions. By directly integrating with inverter portals, PV Doctor eliminates the need for additional hardware, making it easy and cost-effective to onboard. The AI-driven system leverages high-precision local sensors (where available), with satellite data and machine learning algorithms to identify performance anomalies, including, for example:
- Performance ratio trending and behaviour;
- Soiling losses caused by industrial pollution, crops burning, or construction soiling;
- Shading impacts from nearby buildings, vegetation growth, or seasonal changes;
- Grid disturbances that affect system stability in regions with unreliable infrastructure;
- Component failures, such as inverter shutdowns, undetected string faults, or degraded modules.
2. Preventive O&M – Proactive maintenance activities for highest energy yields
For solar asset owners who prefer a hands-off approach, the “PV Doctor’s” Preventive O&M programme ensures that systems remain clean, well-maintained, and fully operational, without the need to involve system owners and facility managers. Routine inspections, scheduled cleanings, and early fault detection help prevent minor issues from escalating into costly failures.
3. Rectification & Special Investigations – Diagnosing and fixing performance losses
Many PV systems suffer from gradual component failures (e.g. potential-induced degradation, PID) or hidden inefficiencies arising, for example, from faulty wiring, loose connections, and insulation failures. System located close to the equator often see module glass staining from water/dust accumulation on solar panels installed at shallow tilt angles. The “PV Doctor” will not rest until the root causes of any underperformance have been identified, irrespective of the complexity of the failure pattern. The team will then work out rectification measures and implement the necessary steps, in close alignment with the client.
4. Repowering – Upgrading aging systems for renewed & increased energy yield
Older PV installations often fail to meet expected outputs due to outdated components (modules with low efficiencies, inverter failures due to ageing) or inefficient system layouts. Repowering revitalises these assets, incorporating the latest technologies, from state-of-the-art modules to modern inverters and realtime monitoring systems. This allows for maximising energy yield on a certain site location and extends system lifespan.
5. Audits & Performance Assessments – Independent 3rd-party verifications
Independent audits or performance assessments are required at many points in time during an asset’s lifecycle, for example during a due diligence process prior to an asset transfer or for certifying electricity generation to verify Renewable Energy Certificates (RECs). The “PV Doctor” generates independent 3rd-party audits and performance assessments using satellite-derived irradiance data, thermal imaging, and detailed electrical analysis to verify energy output, identify discrepancies, and support compliance with
industry standards.
6. Technical Support – Expert guidance for asset owners, developers, and investors
Managing a solar asset (or an entire PV portfolio) requires more than just operational oversight. It demands strategic planning and informed decision-making. Whether it is about evaluating tenders, quality assurance during component selection, construction and testing & commissioning, or preparing for an acquisition (or sale of assets), the “PV Doctor” provides data-backed insights and risk assessments to ensure project success.
DGIST unveils the secret of water-induced degradation in perovskite! Expected to accelerate the commercialization of next-generation optoelectronic materials
A research team led by Professor Jiwoong Yang of the Department of Energy Science & Engineering at DGIST (President Kun-woo Lee) has successfully observed and identified the water-induced degradation mechanism of perovskite, which is a next-generation optoelectronic material, in real time at the atomic scale. This study presents key strategies for enhancing the stability of perovskite materials and is expected to accelerate their commercialization.
□ Perovskite is gaining attention as a next-generation light-emitting material for various optoelectronic devices such as LEDs, solar cells, photodetectors, and quantum devices. Its excellent luminous efficiency and color reproduction makes it highly attractive for future display and energy applications. However, its inherent vulnerability to moisture has been a significant obstacle to commercialization.
□ The research team employed an in-situ liquid-phase transmission electron microscopy (TEM) technique to observe the structural changes of perovskite when exposed to water at the atomic level. They discovered that reaction rates differ depending on the crystal facet, and that specific surfaces selectively dissolve, leading to a gradual transformation from a cubic to a spherical structure. This degradation process was successfully visualized in real time.
□ Furthermore, the team proposed strategies to suppress the surface degradation of perovskite materials. They found that coating nanocrystal surfaces with ligands or hydrophobic polymers that form strong bonds with perovskite effectively prevents structural transformation and significantly slows the overall degradation rate.
□ Professor Yang stated, “This is the first study to visualize the water-induced degradation of perovskite in real time at the atomic level, providing critical insights into the fundamental stability issues of the material. Based on our findings, we anticipate significant improvements in perovskite stability, which will help accelerate its path to commercialization.”
□ This research was supported by the National Research Foundation of Korea through the Nano and Materials Technology Development Program (Materials Global Young Connect), the Korea–U.S. International Joint Technology Development Program of the Korea Institute for Advancement of Technology, and the Future Technology Development Center of Samsung Electronics. The study was jointly conducted by DGIST, Lawrence Berkeley National Laboratory, and the Pohang Accelerator Laboratory, and the results were published in Matter, a world-renowned materials science journal and sister publication of Cell.
- Corresponding Author E-mail Address : jiwoongyang@dgist.ac.kr
Journal
Matter
Article Title
Water-induced degradation mechanism of metal halide perovskite nanocrystals
