Tandem

Researchers at Tokyo City University in Japan have reportedly achieved a new world record power conversion efficiency for a tandem solar cell that combines a perovskite top cell with a copper-indium-gallium-selenide (CIGS) bottom cell. The two-terminal device has an active area of 1 cm² and reached a certified efficiency of 25.14%, with the result independently confirmed by Japan’s National Institute of Advanced Industrial Science and Technology (AIST).

This surpasses the previous record of 24.6% for a perovskite-CIGS tandem, which was set by Germany’s Helmholtz-Zentrum Berlin (HZB) in February 2025, after which groups worldwide had been trying to push the technology beyond the 25% threshold. The Japanese team notes that, until now, this 25% mark had remained out of reach despite intensive international research efforts.

Researchers from China's Huazhong University of Science and Technology, Optics Valley Laboratory, Taizhou University, Nanjing Tech University (NanjingTech), Southern University of Science and Technology, Henan Normal University, Shandong University and the UK's University of Oxford have developed a robust interconnecting layer strategy for all-perovskite tandem solar cells that addresses key stability bottlenecks associated with conventional designs.

All-perovskite tandems have already surpassed 30% power conversion efficiency (PCE) in double-junction configurations, but long-term operational stability, especially under heat and light, remains a major limitation. A central issue lies in the interconnecting layers, which must simultaneously provide high transparency, efficient charge recombination, and chemical robustness. Standard architectures typically rely on a stack of C60/SnOx/ultrathin Au/PEDOT:PSS. However, PEDOT:PSS introduces parasitic absorption and chemical instability due to its acidic and hygroscopic nature, triggering degradation pathways such as iodine formation and Sn(II) oxidation in tin-lead (Sn-Pb) perovskites. At the same time, the inclusion of ~1 nm Au leads to optical losses via plasmonic absorption and can diffuse into the absorber at temperatures around 65°C, further compromising device stability.

Tokyo Chemical Industry (TCI), a global supplier of laboratory chemicals and specialty materials, is offering BrNH3-4PACz materials, an SAM-forming agent, that can be used as a replacement for PEDOT/PSS in tandem perovskite solar cells.

TCI explains that in a tandem perovskite solar cell architecture, a wide-bandgap (WBG) Pb-PSC (the top cell) is placed on top of a narrow-bandgap (NBG) Pb/Sn-PSC (the bottom cell). In NBG-type PSCs, the PEDOT/PSS (HTL) material has a drawback in that it oxidizes Sn2+ Therefore, in the fabrication of PSCs containing Sn (including NBG-type PSCs), it is considered desirable to replace PEDOT/PSS with a self-assembled monolayer (SAM)-forming agent. This has been shown in several research papers, including this 2025 one.

A team of researchers, led by the Chinese Academy of Sciences (CAS), has developed a generalizable strategy to control crystallization kinetics in all-perovskite tandem solar cells, enabling certified power conversion efficiencies of 30.3% in rigid devices and 28.0% in flexible configurations.

Synchronized crystallization drives efficient rigid and flexible perovskite tandems. Image credit: NIMTE

All-perovskite tandems can enable high efficiency and compatibility with low-temperature solution processing. However, their performance has been consistently limited by asynchronous crystallization in multicomponent perovskite systems. This effect arises from mismatched coordination chemistry and crystallization rates among mixed halide systems and Pb²⁺/Sn²⁺ cations, leading to vertical compositional gradients, structural inhomogeneity, and elevated non-radiative recombination losses.

Fraunhofer ISE has inaugurated a new research and development laboratory aimed at accelerating the industrial adoption of perovskite-silicon tandem solar cells. The facility, named “Pero-Si-SCALE,” is designed as an open, industry-accessible platform to help bridge the gap between laboratory-scale innovation and large-scale manufacturing.

Image credit: Fraunhofer ISE

The Pero-Si-SCALE facility focuses on transferring early-stage innovations (Technology Readiness Levels 1-4) into industry-relevant processes and formats. It enables scaling of tandem cell designs to large wafer sizes - up to 210 x 210 mm - using high-throughput, industry-standard manufacturing techniques. In addition to process development, the lab offers comprehensive characterization and analysis capabilities, as well as support for integrating tandem cells into full photovoltaic modules.

Researchers at Nanjing University, the Australian National University, North China Electric Power University and Beijing Institute of Technology have demonstrated thermally stable, MA‑free all‑perovskite tandem solar modules by using a p‑π conjugated additive, semicarbazide hydrochloride (SHCl), to control the crystallization of FACs (FA‑Cs) Pb‑Sn perovskites.

(A) Photograph of the all-perovskite tandem module. (B) Cross-sectional SEM image of the tandem solar device. Image from: Science Advances

All‑perovskite tandems already reach ~25% PCE at module scale, but narrow‑bandgap Pb‑Sn subcells typically rely on thermally unstable methylammonium (MA), and simply replacing MA with Cs‑rich FACs compositions causes rapid, nonuniform crystallization that degrades large‑area film quality. The team tackles this by introducing SHCl into FACs Pb‑Sn precursor solutions, where SH⁺ and Cl⁻ ions cooperatively regulate nucleation and growth: SHCl reacts with CsI (SHCl+ CsI → SHI + CsCl), forming CsCl and SHI, and strongly coordinates with Cs⁺ via its carbonyl group, which lowers Cs solubility, increases supersaturation, and drives a short “burst” of homogeneous nucleation followed by slower crystal growth.

Risen Energy recently announced progress in its heterojunction (HJT) silicon-based perovskite tandem cell technology. Reportedly certified by authoritative institutions, the company’s 1 cm² tandem cell achieved a photoelectric conversion efficiency of 31.95%, with an open-circuit voltage of 1.988V.

This achievement is built upon the company’s long-term expertise in both HJT and perovskite technical routes. As one of the early pioneers in HJT industrialization, Risen Energy has mastered a comprehensive technical ecosystem, ranging from high-efficiency N-type HJT ground-based photovoltaic products to P-type HJT cells designed for the harsh environments of outer space.

Perovskite manufacturer Huarou PV has reported a power conversion efficiency of 31.73% achieved on its all-perovskite tandem solar cell, which has been certified by the National Photovoltaic Industry Measurement and Test Center (NPVM).

The cell demonstrated an open-circuit voltage of 2.224 V. This follows the company’s earlier announcement of 27.98% efficiency for a single-junction perovskite cell under standard illumination.

Solx, a U.S.-based solar manufacturer, and Caelux, a U.S.-based perovskite solar developer, have announced a five-year, 3-gigawatt (GW) strategic partnership and unveiled their breakthrough U.S-made high-performance solar module. 

The collaboration integrates Caelux’s advanced energy-producing glass into Solx’s Aurora™ platform, creating a solar module with double power generation layers (hybrid tandem), enabling increased efficiencies of 28% and delivering significantly more power than conventional silicon-only modules.

Swansea University is leading a new international partnership to develop affordable, next-generation all-perovskite tandem solar cells tailored for African climates, aiming to support long-term energy access and future local manufacturing across East Africa. The SOLACE (Solar Alliance on Clean Energy) project links researchers in the UK, Kenya, Rwanda and Tanzania to co-develop advanced perovskite photovoltaic technologies while building shared skills, training opportunities and research expertise in the region.

Project co-lead Dr. Francis Otieno with fourth-year physics students at Maseno University, Kenya. Credit: Maseno University

Access to reliable, low-cost and clean electricity remains a major constraint on economic development, healthcare and education across many African countries. In Kenya, Rwanda and Tanzania, expanding energy access is critical for rapidly growing populations and for strengthening climate resilience. Existing crystalline silicon technologies dominate the global market but are relatively expensive and energy-intensive to manufacture, and they have not yet been produced at scale within Africa. All-perovskite tandem solar cells are seen as a promising alternative, as they can be processed at low temperatures using solution-based methods, significantly reducing manufacturing costs and energy demand. By combining two perovskite absorbers in a tandem architecture, the SOLACE team aims to achieve higher efficiencies than single-junction devices while maintaining compatibility with scalable, low-cost production routes.