Tandem - Page 19

Researchers from the Australian National University (ANU) have quantified losses in PV'based solar hydrogen generation systems and have proposed a series of loss-mitigation techniques to improve solar'to'hydrogen (STH) conversion efficiencies.

The scientists identified STH efficiency as the crucial factor that needs to be improved to reduce the overall costs of PV-powered hydrogen generation. 'The U.S. Department of Energy has set a target of 20% STH efficiency by 2020 and an ultimate goal of 25%, to ensure the economic viability of PV'based solar hydrogen generation for large scale hydrogen production,' they specified, adding that current efficiency levels range from 10-15%.

A consortium of academic research teams and private companies led by Hanwha Q Cells, a major photovoltaic manufacturer in South Korea, was selected for a state project to commercialize tandem perovskite silicon solar cells.

In an effort to widen the technology gap with China, South Korean companies and researchers have tried to develop new solar energy technologies like tandem cells that build 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 though each cell.

Researchers at HZB have published their recent work, reporting its current world record of 29.15% efficiency for a tandem solar cell made of perovskite and silicon. The tandem cell provided stable performance for 300 hours ' even without encapsulation. To accomplish this, the group, headed by Prof. Steve Albrecht, investigated physical processes at the interfaces to improve the transport of the charge carriers.

In the beginning of 2020, a team headed by Prof. Steve Albrecht at the HZB broke the previous world record for tandem solar cells made of perovskite and silicon (28.0%, Oxford PV), setting a new world record of 29.15%. Compared to the highest certified and scientifically published efficiency, this is a significant step forward. The new value has been certified at Fraunhofer ISE and listed in the NREL chart. Now, the results have been published in the journal Science with a detailed explanation of the fabrication process and underlying physics.

Fraunhofer Institute for Solar Energy Systems ISE researchers have examined the question of which silicon bottom cell will be most suitable for use in tandem cells. The team evaluated multiple silicon cell concepts based on both cost and efficiency in serving as the bottom layer in a perovskite-silicon tandem cell.

Investigated perovskite silicon tandem concepts featuring four different silicon bottom cells (P E RC, TOPerc, TOPCon2, and SHJ) and two different interconnection concepts (ReCO and SiT). Image from article

The study, based on both simulation and experimental work, details advantages to various approaches with the silicon cell and concludes that in almost every case, perovskite-silicon tandem cells have the potential to bring solar costs down below what could be achieved with silicon alone.

Sweden-based perovskite-based PV start-up Evolar has announced an investment from Norwegian renewables investor Magnora as it targets rapid commercialization of its technology.

Evolar has been researching the development of perovskites in solar cells, and Evolar now intends to help commercialize the technology. Evolar's approach is to add a perovskite-based thin-film layer to cells to create a tandem solar cell, which the company said is expected to increase module efficiency by five percentage points.

Researchers at HZB have reported findings from their recent work: printing and exploring different compositions of caesium based halide perovskites (CsPb(Br_xI_1'x)₃ (0 ≤ x ≤ 1)).

In a temperature range between room temperature and 300 Celsius, the team observed structural phase transitions influencing the electronic properties. The study presents a quick and easy method to assess new compositions of perovskite materials in order to identify potential candidates for applications in thin film solar cells and optoelectronic devices.

Japan-based global conglomerate Toshiba, announced that it would not take any new orders for the construction work of coal-fired thermal facilities. The company is planning to shift towards renewable energy solutions.

According to Toshiba, the company will support the infrastructure sector's transformation to achieve decarbonization goals. In addition to activities involving windmills and development of secondary batteries, Toshiba aims to commercialize its newly developed next-generation tandem and perovskite solar cells by 2025.

Oxford PV, currently involved in building a manufacturing facility in Brandenburg an der Havel for its silicon perovskite tandem solar cells (in which it is investing around €44 million), has received €8.8 million funding from the state Ministry of Economics in Potsdam for this project.

'I am delighted that Oxford Photovoltaics has brought the solar technology developed by the company itself to market maturity and that it will soon start with industrial series production here in Brandenburg,' said Brandenburg Minister for Economic Affairs Jörg Steinbach. 'The decision by Oxford PV to expand the production facility in Hohenstücke is a clear commitment to our community.'

KAUST researchers have developed a perovskite ink tailor-made for a mass manufacturing process called slot-die coating, producing PSCs that captured solar energy with high efficiency. The ink could also be coated onto silicon to create perovskite/silicon tandem solar cells.

The planar p-i-n device architecture of the perovskite solar cell employed in the study. Image credit: KAUST

PSCs made in research labs are typically made by spin-coating, which is unsuited to mass manufacture. Slot-die coating, in contrast, is a manufacturing technique used industrially for many years. 'The process involves continuously and precisely forcing an ink through a narrow slit that is moved across the substrate to form a continuous film,' Anand Subbiah, a postdoc in Stefaan De Wolf's lab, said. 'This high-throughput technique would allow for roll-to-roll fabrication, similar to printing newspapers.'

KAUST researchers have conducted outdoor tests, that have shown that an increase in temperature affects the performance of a tandem perovskite/silicon solar cell due to voltage losses aw well as current mismatch between the two sub-cells.

The energy yield of two-terminal tandem cells is maximized when the two sub-cells produce the same current at the maximum power point. However, when one of the two devices generates less current than the other, and current mismatch between the sub-cells occurs, the overall device's current is affected.