Transparency

Researchers from the University of Rome Tor Vergata, Hellenic Mediterranean University, Université Grenoble Alpes (CNRS), Halocell Europe, CHOSE, ENEA, 3SUN - Enel Green Power and BeDimensional have developed a scalable four-terminal (4T) perovskite/silicon tandem architecture that combines high efficiency, semi-transparency and real-world stability by engineering a field effect junction directly inside the perovskite absorber. 

a Layout of the semi-transparent 2D material-based PSMs. Each module is composed by 24 series-connected solar cells with an active area of 2.49 cm². The total active area is 60 cm² while the aperture area (comprising the interconnection areas) is about 63 cm². b Demonstrator 1 (DEM1) perovskite/Si tandem panel. Each building block is composed of four parallel-connected semi-transparent perovskite modules stacked above the M2 Si-HJT bifacial cell (provided by 3SUN). c, d Pictures of the front and back side of the laminated tandem DEM1. Image from: Nature Communications

The work targets industrially relevant, large-area modules compatible with standard silicon wafer dimensions and production lines, addressing key bottlenecks in the commercialization of perovskite/Si tandems such as scalability, efficiency loss on upscaling, and outdoor durability.

Researchers from the Indian Institute of Technology Bombay and Linköping University have reported a four‑terminal (4T) silicon-perovskite tandem solar cell with a power conversion efficiency of 30.2%. The device combines an optimized transparent perovskite top cell with a monocrystalline n‑type TOPCon silicon bottom cell that delivers 25.5% efficiency on its own.

Efficient spectral utilization in tandem architectures requires careful bandgap tuning of the perovskite absorber. However, shifting the bandgap up or down often introduces open‑circuit voltage (VOC) losses, which are commonly attributed to misalignment at the charge‑transport interfaces. The study investigates whether this conventional explanation fully accounts for the observed voltage deficits.

Researchers from the National University of Singapore and AGH University of Krakow have developed a novel fabrication strategy for double-sided tunnel oxide passivated contact (DS-TOPCon) silicon bottom cells, designed for use in perovskite/silicon tandem (PST) solar cells. The team demonstrated that carefully controlled heated indium tin oxide (ITO) deposition can significantly reduce sputtering-induced damage while enhancing conductivity and transparency - two critical requirements for efficient tandem integration.

In DS-TOPCon architectures, both the front and rear surfaces of the silicon wafer feature passivating silicon oxide (SiOx)/polycrystalline silicon (poly-Si) stacks, replacing the conventional single-sided (SS-TOPCon) structure. The result is a fully passivated, symmetric cell that minimizes recombination losses and raises the open-circuit voltage. This approach also provides improved carrier selectivity and mechanical stability - qualities that make DS-TOPCon particularly well suited to high-efficiency, monolithic tandem devices.

Researchers from Kyung Hee University and Hyundai Motor Group have developed an AI-based inverse design strategy that enables full-color, high-efficiency semitransparent perovskite solar cells for applications such as solar windows and vehicle glazing. The work introduces a modelling-guided framework that integrates all-dielectric multilayer coatings - composed of alternating zinc sulfide (ZnS) and magnesium fluoride (MgF₂) - into perovskite photovoltaics, allowing user-defined transmitted colors with minimal optical loss.

Photographs of semitransparent PVSK PVs. Left: uncoated Right: ZnS/MgF2-coated. Image from: Opto-Electronic Advances

Unlike conventional color-tuning methods that rely on metallic or absorptive films, the team’s approach employs transparent interference coatings designed through a digital optimization loop. Each layer sequence is encoded as a binary string and evaluated by a factorization machine-based surrogate model trained on optical simulations. The optimization, expressed as a quadratic unconstrained binary optimization (QUBO) problem, identifies the precise ZnS/MgF₂ configurations that meet specific color coordinates and average visible transmittance (AVT) targets.

A recent study by researchers at Israel's Hebrew University of Jerusalem reports the development of a semi-transparent, color-tunable perovskite solar cell designed for integration into surfaces such as architectural glass and flexible substrates where conventional panels are not suitable. The devices are fabricated using a low-temperature process that combines plasma-assisted deposition of the electron transport layer with inkjet printing of 3D polymer pillars from a solvent-free, UV-curable monomer.

Schematic presentation of the main steps involved in the fabrication of a colorful, semi-transparent, flexible perovskite solar cell. Image from : EES Solar

The work, led by Prof. Shlomo Magdassi and Prof. Lioz Etgar from the Institute of Chemistry and the Center for Nanoscience and Nanotechnology, presents a method for controlling optical and mechanical properties without modifying the perovskite absorber layer. Optical transparency is adjusted by the spacing of the micrometric polymer pillars, which act as “optical holes” within the perovskite layer, enabling a balance between active area, average visible transmittance, and mechanical robustness.

Researchers from the Indian Institute of Technology Bombay have demonstrated a room-temperature, non-destructive method for depositing amorphous indium zinc oxide (a-IZO) transparent electrodes in perovskite solar cells, providing a step forward in device durability and performance compared to conventional indium tin oxide (ITO) electrodes. 

Their study specifically compared amorphous IZO (a-IZO) with polycrystalline ITO (c-ITO) as rear transparent electrodes in superstrate-architecture perovskite solar cells.​ The transparent perovskite solar cells (T-PSCs) were fabricated using a n–i–p device stack, composed of c-ITO or a-IZO rear transparent electrode, a molybdenum(VI) oxide (MoO₃) buffer layer, Spiro-MeOTAD hole transport layer, a perovskite absorber, a tin(IV) oxide (SnO₂) electron transport layer, and a fluorine-doped tin oxide (FTO) front electrode. This device architecture enabled a direct comparison of the performance and interface characteristics associated with each electrode material.​

Researchers from the CitySolar project have announced an efficiency record for transparent solar cells. By combining organic solar cells with perovskite-based ones, the scientists were able to achieve an efficiency of 12.3%.

These cells could be used for building-integrated photovoltaics, transforming windows into solar panels. “Transparent solar cells could be the next big step in building-integrated energy solutions,” said Professor Morten Madsen from the University of Southern Denmark, who was one of the key researchers behind the breakthrough. “The large glass facades found in modern office buildings can now be used for energy production without requiring additional space or special structural changes... This represents a massive market opportunity.”

EneCoat Technologies has announced a conversion efficiency of over 30% with a 4-terminal tandem cell consisting of stacked perovskite and crystalline silicon solar cells in a joint development project with Toyota Motor Corporation. 

This achievement underscores the profound research and development capabilities of both companies in the field of perovskite solar cells and accelerates the practical application of high-efficiency solar cells, which is the objective of the joint development project. In this project, the two companies focused on the transmittance of perovskite solar cells and succeeded in improving the infrared transmittance to 81%.

Researchers from Pakistan's University of Engineering & Technology (UET) and National University of Technology have reported the use of manual screen printing to fabricate semi-transparent, scalable perovskite solar modules without the requirement for numerous laser-scribing steps. 

A carbon-based, hole-transport-layer-free perovskite solar module with a power conversion efficiency of 11.83% was manufactured, with an active area of 900 cm². Accelerated testing was done in settings with elevated humidity, high sun irradiation, and harsh temperatures to determine whether these modules are ready for the market. 

The fabrication of perovskite/Si tandem solar cells often encounters the challenge of selecting a suitable sputtering buffer layer (SBL) to prevent damage during the transparent electrode deposition. In their recent work, researchers from China's Northwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene (NPU), Chinese Academy of Sciences and Ningbo New Materials Testing and Evaluation Center Co. developed a perovskite-silicon tandem solar cell that uses an indium oxide sputtering buffer layer to protect the perovskite absorber and the electron transport layer from damages that might occur during the electrode deposition process. The new layer not only granted this protection but also showed strong optical and electrical properties. 

The team introduced the indium oxide (In₂O₃) buffer layer via e-beam deposition to fabricate semi-transparent perovskite solar cells. The optical transmittance and electrical conductivity of In₂O₃ highly depend on the deposition rate. High deposition rate results in high ratio of metallic indium in the film, which causes severe parasitic absorption. A 20 nm-thick In₂O₃ film deposited at lower rate demonstrated high conductivity, transmittance and robust protection during sputtering.