Researchers from Germany's Helmholtz-Zentrum Berlin (HZB) and Institute for Solar Energy Research (ISFH) have reported that passivated emitter and rear cell (PERC) tech can be suitable as a basis for tandem cells with perovskite top cells.

PERC cells are usually used in mass production of silicon solar cells, and while the efficiency of the study's tandem cells is still below that of optimized PERC cells alone, the team estimates that it could be increased to up to 29.5% through targeted optimization.

Researchers from the Wuhan Institute of Technology and Wuhan University have investigated key factors for realizing high-performance narrow-bandgap Pb-Sn perovskite solar cells (PSCs) via numerical simulations.

The team studied both extrinsic and intrinsic factors of efficient narrow-bandgap Pb-Sn perovskite solar cells. The effects of extrinsic factors on device performance predicted that a p-i-n structure along with appropriate charge transport layers is superior to an n-i-p structure, benefiting from a better energy band alignment. The key intrinsic factors that were studied demonstrated that surface defect density, body defect density, and film thickness of perovskite absorbers play a pivotal role in determining device performance.

Researchers from the University of Amsterdam and NWO-Institute AMOLF have examined the efficiency gain offered by perovskite/silicon tandem solar cells containing several semiconductors with diverse energy gaps, with a spectrum splitter added between the top and bottom terminals.

This design allows the tandem solar cells to be responsive to a wider region of the sunlight's spectrum. However, such cells usually deal with ineffective light trapping and management due to parasitic light absorption in inactive layers and reflection between layers. Various studies have looked into these issues, yet the idea of spreading sunlight in the tandem subcells with controlled spectral splitting was not adequately investigated.

Researchers from Professor Tan Hairen group at Nanjing University in China recently developed all-perovskite tandem solar cells with a conversion efficiency of 26.4%, certified by JET.

The team developed ammonium-cation-passivated Pb-Sn perovskites with long diffusion lengths, enabling subcells with an absorber thickness of ~1.2 μm. Molecular dynamics simulations suggest that widely-used phenethylammonium (PEA) cations are only partially adsorbed on the surface defective sites at perovskite crystallization temperatures. The passivator adsorption is predicted to be enhanced using 4-trifluoromethyl-phenylammonium (CF3-PA), which exhibits a stronger perovskite surface-passivator interaction than does PEA.

A consortium led by Hanwha Q Cells, a leading manufacturer of photovoltaic solar cells in South Korea, has been selected for a three-year state project to develop and commercialize perovskite crystalline silicon solar cells with high durability and high efficiency by using tandem cell technology that builds perovskite on top of silicon solar cells.

Tandem solar cells can be individual cells or connected in series, which are simpler to fabricate but the current is the same through each cell. Hanwha Q Cells said the consortium involving three private companies, two research bodies and three universities has signed an agreement with the state-run Korea Institute of Energy Technology Evaluation and Planning (KETEP) to develop module process technologies.

Uppsala University spinoff Evolar has entered into a joint development project with an undisclosed Indian silicon solar module manufacturer to develop highly efficient perovskite/silicon tandem solar modules for the South Asian market.

'Evolar is developing a unique perovskite-based PV power booster technology that adds 25 percent power to conventional solar panels. Moreover, it is easy to integrate the perovskite thin film process into current production set-ups. We firmly believe that the combination of our perovskite-based technology and this manufacturing partnership, can play a key role in strengthening India's domestic solar module supply,' says Mats Ljunggren, CEO of Evolar AB.

Three HZB teams, led by Prof. Christiane Becker, Prof. Bernd Stannowski and Prof. Steve Albrecht, have jointly managed to bring the efficiency of perovskite silicon tandem solar cells to a new record value of 29.80%. This result has been officially certified by Fraunhofer ISE CalLab and is documented in the NREL-charts.

The perovskite silicon tandem cell is based on two innovations: A nanotextured front side ( left) and a back side with dielectric reflector (right). © Alexandros Cruz /HZB

Several HZB groups have been working intensively since 2015 on both the perovskite semiconductors and silicon technologies and the combination of both into innovative tandem solar cells. In January 2020, HZB had achieved a record 29.15 % for a perovskite silicon tandem solar cell. Then, also in 2020, the company Oxford PV was able to announce a certified efficiency of 29.52%. Since then, the race for new records has been on. "An efficiency of 30% is like a psychological threshold for this fascinating new technology which could revolutionize the photovoltaic industry in the near future," explains Steve Albrecht, who is working on perovskite thin films at the HySPRINT lab at HZB. Bernd Stannowski, group leader for silicon technology, adds: "I would particularly emphasize the good cooperation between the different groups and institutes at HZB. This is how we managed to develop these new tandem solar cells entirely at HZB and once again get the world record."

A research team, led by Germany's Fraunhofer Institute for Solar Energy Systems (ISE), studied two stages of cell manufacturing that are among the most in need of optimization due to growing concerns over the availability of the commonly used indium and silver: transparent conductive oxide deposition and cell metallization.

The research takes processes used in silicon heterojunction (HJT) cell manufacturing as a starting point, and examines how the addition of a perovskite top cell would change the requirements for the rest of the cell structure.

Solliance recently announced that a collaboration with the M2N group of René Janssen at University of Technology Eindhoven has resulted in two world-records for 4T perovskite tandems.

The partners reported that they further optimized the wide-bandgap (1.69eV) perovskite cells with high near-infrared transparency for 4T tandem applications. The perovskite cell has reached a stabilized efficiency of 17.8% during 5-min maximum-power-point tracking. In combination with the Panasonic silicon bottom cell, a new world-record 4T perovskite/Si tandem efficiency of 29.2% was realized.

The US Department of Energy (DoE) awarded nearly $40 Million for grid-decarbonizing solar technologies projects. The DoE awarded the funds to 40 research projects, several of which are perovskite related. We'll list the perovskite projects (which were awarded a total of $1.25 million) below.

The DoE also issued a request for information (RFI) to gather input on efficiency, stability and replicability performance targets for perovskite photovoltaic devices that could be utilized to demonstrate technical and commercial readiness for future funding programs.