Article last updated on: Jan 08, 2018

Silicon-perovskite tandem solar cells reach record efficiency of 25.2%

EPFL the CSEM PV-center researchers have combined silicon and perovskite to create solar cells with the resulting efficiency of 25.2%, in what is regarded as a record for this type of tandem cell. Their innovative yet simple manufacturing technique could be directly integrated into existing production lines, and efficiency could eventually rise above 30%.

EPFL team designs record efficiency tandem cell image

The researchers explain that creating an effective tandem structure by superposing two materials is no easy task. "Silicon's surface consists of a series of pyramids measuring around 5 microns, which trap light and prevent it from being reflected. However, the surface texture makes it hard to deposit a homogeneous film of perovskite," explains Quentin Jeangros, who co-authored the paper. A common problem in such cells arises from the fact that when the perovskite is deposited in liquid form, it accumulates in the valleys between the pyramids while leaving the peaks uncovered, leading to short circuits. The team tackled this problem by using evaporation methods to form an inorganic base layer that fully covers the pyramids. That layer is porous, enabling it to retain the liquid organic solution that is then added using a thin-film deposition technique called spin-coating. The researchers subsequently heat the substrate to a relatively low temperature of 150°C to crystallize a homogeneous film of perovskite on top of the silicon pyramids.

A simple process can turn sea urchin skeletons into perovskites

Researchers at AMOLF have found a way of turning calcium carbonate structures, such as a sea urchin skeleton, into perovskite materials, by modifying the composition of the material. The team explained that "the experiment involves no more than dripping two liquids over the calcium carbonate structure. The conversion is complete within a couple of minutes. If you shine a UV lamp on the structure, you can see the conversion taking place in front of your eyes: The sea urchin skeleton, which initially appears blue under the lamp, changes into a bright green structure with each drop".

AMOLF team turns calcium carbonate into perovskites imageA sand dollar skeleton gradually converting into a light emitting perovskite

The researchers estimate that the perovskite microstructures made in this process result in more stable materials. They therefore state that solar cells made from this material should last longer. "In addition, we can produce perovskite structures in every desired color. This means that the material could also be used for LEDs in various applications, such as screens," says the research team.

EU establishes the MAESTRO project - a €4 million program for perovskite solar materials research

The European Commission has established a new research training network, led by the University of Bath, to make perovskites "truly exploitable" and make perovskite-based devices commercially viable. The new program, called MAESTRO, has been given €4 million in funding and has begun hiring researchers to gain new knowledge and provide innovation in the exploitation of perovskite materials.

A trans-European project, MAESTRO is an inter-sectoral and multidisciplinary network of 10 academic and seven industrial partners from nine EU and EU-Associated countries: the UK, Italy, Spain, Greece, Germany, Poland, Lithuania, Israel and Switzerland.

A novel form of perovskite materials shown to improve the stability of perovskite solar cells

Researchers from the Institute of Physical Chemistry of the Polish Academy of Sciences and the Faculty of Chemistry of Warsaw University of Technology have designed what they consider to be an improved version of a perovskite, containing in the crystal structure a relatively large organic ion, a guanidinium cation. Lab tests at the EPFL have reportedly shown that photovoltaic cells made of the new perovskite work more efficiently than the cells prepared using its original form.

The guanidinium cation was incorporated into the crystal structure of the classic perovskite using a ‘solvent-less’ mechanochemical approach. The experiments proved that from many aspects the new, modified perovskites are clearly better than the parent (CH3NH3)PbI3.

ANSER team develops a new way to protect PSCs from water

Researchers at the Argonne-Northwestern Solar Energy Research Center (ANSER) have developed a new way to protect perovskite-based solar cells from water and stabilize them against heat. By carefully growing an ultrathin layer of metal oxide on a carbon coating, the researchers made a perovskite device that worked even after exposing it to a stream of water.

ANSER develops a new way to protect PSCs from water image

Solar cells are made up of layers, each with a specific duty. The perovskite layer absorbs sunlight, which can excite an electron. The electron could go back to where it started, unless it can be successfully extracted out of the absorbing layer quickly. For this device, the researchers placed a layer of PC61BM, a carbon-based material, on top of the perovskite, which has two roles.