Transparency

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. 

Semi-transparent solar cells are appealing for many different applications such as building-integrated photovoltaics (BIPVs), tandem solar cells and in wearable electronics. Perovskites could be ideal for semi-transparent applications as they are versatile and easy to optimize.

Semi-transparent perovskite solar cells (ST-PSCs) must try to maximize efficiency and transparency. Methods such as bandgap engineering, thinning perovskite layers, and creating discontinuous structures are being developed to improve their performance. However, challenges still remain with ST-PSC development, such as phase stability and defect management.

An EU-funded Laperitivo project was launched earlier this month, focused on manufacturing large-area stable perovskite solar modules. Laperitivo stands for “large-area perovskite solar module manufacturing with high efficiency, long-term stability, and low environmental impact.” The project aims to achieve 22% efficiency for 900 cm² opaque panels and 20% for semi-transparent modules with more than 95% bifaciality.

The team will focus, among other things, on solving scalability challenges, to promote large-scale mass production with minimized losses. The abstract of the project’s EU funding paper also states that: “Indoor and outdoor field tests will be performed to monitor module reliability. Safety, circularity, and sustainability will be assessed to demonstrate products with minimized environmental impact.”

Reports suggest that a solar power project in China, which utilizes translucent perovskite panels, has recently been connected to the grid in Gansu Province. This project was developed through a collaboration between the Electric Power Science Research Institute of the China State Grid Gansu Electric Power Company and a renewable energy subsidiary of China Datang Corp.

It was stated that the perovskite solar cells were processed to be translucent by the application of special graphical structures, including grind lines and dots, on the perovskite film. The specific structures are the result of precise control of parameters, including exposure time and depth. The graphical structures allow for the optimization of the light propagation path within the cell, thereby enhancing light absorption efficiency and improving the cell’s photoelectric conversion performance.

Researchers from Austria's Johannes Kepler University Linz have developed lightweight, thin (<2.5 μm), flexible and transparent-conductive-oxide-free quasi 2D perovskite solar cells by incorporating alpha-methylbenzyl ammonium iodide into the photoactive perovskite layer. 

The team fabricated the devices directly on an ultrathin polymer foil coated with an alumina barrier layer to ensure environmental and mechanical stability without compromising weight and flexibility.