07-21 Oxford PV perovskite tandem solar cell

[Image above] Oxford PV set a new world record for the efficiency of a commercial-sized perovskite tandem solar cell in May 2023. Credit: Oxford PV

By Laurel Sheppard

The market for solar energy is growing quickly, with installed power capacity exceeding 1,000 TWh in 2021. Though prices have dropped significantly in recent years, power conversion efficiency remains a limitation due to continued reliance on silicon, the traditional photovoltaic material.

The average power conversion efficiency for current silicon-based solar panels is about 22%. Though a record efficiency of 26.81% was achieved by Chinese photovoltaics company LONGi in November 2022, the maximum theoretical efficiency for silicon-only solar cells is just 29%—a maximum we are quickly approaching.

To increase efficiency beyond 29%, other materials besides silicon will be needed. Perovskites, a class of materials with the same crystal structure as calcium titanate (CaTiO3), are attracting attention because of their high light absorption efficiency and ease of fabrication. They also can be made from inexpensive raw materials.

In December 2020, researchers at Technical University Berlin demonstrated the power of perovskites when they overcame the silicon-only efficiency limit. They achieved a record 29.15% efficiency with a perovskite–silicon tandem solar cell.

The potential of perovskites, both in combination with silicon and alone, is gaining steam. Below is a snapshot of some of the biggest advancements in this field in recent months.

A year of records for perovskite–silicon tandem solar cells

In the past year, several groups have set new efficiency records for perovskite–silicon tandem solar cells.

In October 2022, a team of researchers from the Netherlands achieved 30% efficiency for the first time with a four-terminal device. Two months later, German researchers at Helmholtz-Zentrum Berlin achieved 32.5%, an efficiency which was officially confirmed by the European Solar Test Installation (ESTI) and the National Renewable Energy Laboratory.

In April 2023, scientists led by King Abdullah University of Science and Technology achieved 33.2% efficiency. They almost immediately surpassed this record in May with an ESTI-certified efficiency of 33.7%.

In June 2023, LONGi announced it had achieved a close second-highest efficiency with an ESTI-certified 33.5%.

In May 2023, Oxford PV, a spinoff company from Oxford University, announced it achieved a record 28.6% efficiency for a commercial-sized tandem solar cell. This record, which was independently certified by Fraunhofer ISE, is more than 1.5% above Oxford PV’s previous record for a device produced on their world-first volume manufacturing line for perovskite-on-silicon tandem solar cells.

According to a Reuters article, Oxford PV plans to commercially launch a tandem solar cell later this year, with a predicted conversion efficiency of 27% and energy yield of 24%.

There still is much room for growth with perovskite–silicon tandem solar cells. According to that same Reuters article, the maximum theoretical efficiency for these cells is 43%.

Developments in all-perovskite solar cells

In addition to perovskite–silicon tandem solar cells, there is also research taking place on all-perovskite solar cells. These cells are expected to provide more flexibility, be lighter weight, and have a lower environmental impact than cells that rely on silicon wafers.

In December 2022, researchers led by East China Normal University reported an inverted perovskite solar cell with the highest efficiency (22.15%) and highest fill factor (83.92%) to date. Key to their success was using the molecule daminozide as an interlayer and additive, which passivated defects at the interface as well as in the perovskite bulk.

In May 2023, researchers at the University of Tabriz in Iran and Bilkent University in Turkey used numerical simulations to show how an inverted perovskite solar cell could achieve an efficiency of 24.83% efficiency (with fill factor of 79.4%) depending on the bilayer configuration.

In June 2023, Nanjing Tech University researchers nearly achieved such a high efficiency in real life by fabricating a perovskite solar cell with a unique “Mortise-Tenon” structure. Their cell, which was created via a joining method typically used in woodworking, demonstrated a 24.55% efficiency.

Just a few days later in June, a different study by Nanjing University researchers reported a record-high efficiency notably surpassing these other studies with a certified 28.0% efficiency (with fill factor of 82.6%.). The cells, which were based on a 3D/3D bilayer perovskite heterojunction, retained more than 90% of their initial performance after 600 hours of continuous operation under simulated one-sun illumination.

What about durability? Extending the lifetime of all-perovskite solar cells

Despite all the potential benefits of all-perovskite solar cells, the cells’ poor durability in real-world conditions hinders commercialization. So, improving durability is a main focus for studies on this technology.

Surface defects are considered the main factor affecting all-perovskite solar cell durability. In December 2022, researchers at Oxford University and Exciton Science demonstrated a new way to create perovskite solar cells with fewer structural and energetic defects. The key was removing the solvent dimethyl-sulfoxide and introducing dimethylammonium chloride as a crystallization agent. This substitution allowed the researchers to better control the intermediate phases of the perovskite crystallization process, leading to thin films of greater quality and enhanced stability.

Back in February 2022, researchers at King Abdullah University of Science and Technology succeeded in creating heat–stable inverted perovskite solar cells based on 2D/3D heterojunctions. Their cells retained more than 95% of their initial 24.3% efficiency after more than 1,000 hours in damp-heat test conditions (85°C and 85% relative humidity).

In May 2023, joint research at Fudan University in China and the University of Victoria in Canada placed a chemical coating on their perovskite solar cells to form covalent bonds with the organic components in perovskites. The coated solar cell retained 98.6% of its initial certified 24.02% efficiency after 1,000 hours of operational tests.

In June 2023, National University of Singapore researchers announced that their inverted perovskite solar cells achieved a stabilized efficiency of 24.35% thanks to the introduction of a novel interface material. According to the announcement, this efficiency is considered a world record for solar cells with an active area of 1 cm2.

With perovskite solar cell developments occurring at such a rapid speed, it will be no surprise if another record is broken in the coming months.