A novel concept for photovoltaics that exploits the ability of products to exist in various crystalline phases

• The group of Prof. Yana Vaynzof at the Integrated Center for Physics as well as Photonic Materials (IAPP) and also the Center for Advancing Electronics Dresden (cfaed) at Technische Universität Dresden has demonstrated a novel concept for solar cells that exploits the ability of materials to exist in various crystalline phases. The relevant study has actually now been released in the journal Nature Energy.

The purpose of a photovoltaic cell is to convert sunlight right into electrical power. By absorbing the sunlight, pairs of cost service providers are produced and then need to be led to the contrary sides of the photovoltaic diode to produce electric existing. To facilitate this procedure, the majority of solar cells consist of a heterojunction that offers a beneficial energetic landscape to drive the charges to be separated.

For example, silicon solar cells form a heterojunction by electrically doping each side of the tool, developing a p-n joint. Organic solar cells, on the other hand, rely on mixing various sorts of products (donor as well as acceptor) to create a bulk heterojunction. Nevertheless, these concepts are commonly not applicable to emerging classes of novel photovoltaic products.

Prof. Vaynzof and also her group have now revealed an entirely new concept for the development of a heterojunction for photovoltaics. To do so, the researchers make the most of the truth that materials can commonly exist in various architectural arrangements, described crystalline phases.

This phenomenon, called polymorphism, suggests that the same product can exhibit various properties, depending on the particular arrangements of atoms and also molecules in its framework. By interfacing two such phases of the same material, Prof Vaynzof and also her group showed for the very first time the development of a phase heterojunction solar cells. Especially, the researchers chose a caesium lead iodide perovskite-- a very reliable solar cell absorber material-- in the beta and also gamma phases to realize their new concept.

"The optical and also electronic buildings of caesium lead iodide in its beta and gamma phase are different from each various other," describes Prof. Vaynzof. "By putting a gamma-perovskite in addition to the beta-perovskite we had the ability to fabricate a phase heterojunction solar cell, that is substantially a lot more reliable as contrasted to solar cells that are based on single phase perovskites." The researchers show in their study, that the leading layer of gamma-phase affects the performance of the solar cells in several methods.

"Even slim layers of gamma-perovskite led to a performance enhancement due to the passivation of defects at the surface area of the bottom layer. Thicker layers of gamma-phase led to significant improvement in all of the photovoltaic efficiency criteria with the champ tool reaching a power conversion effectiveness of over 20%," includes Ran Ji, the lead writer of the research.

"Advanced spectroscopic evaluation revealed that this improvement in performance is connected with increased light absorption as well as the development of a helpful energised positioning between the two phases," describes Prof. Vaynzof.

Notably, the researchers validated that the phase heterojunction remains stable during solar cell procedure and even supresses ion migration in the solar cell absorber, settling an usual trouble for perovskite materials.

To understand the phase heterojunction concept, the scientists utilized 2 different construction processes for the top and also the bottom layers. This versatile strategy opens the path to the formation of various other such frameworks in the future. "We really hope that this novel concept integrated with an easy fabrication route for phase heterojunctions will certainly be applicable additionally to a variety of material systems in a series of electronic as well as optoelectronic tools," claims Prof. Vaynzof.

Since numerous semiconductor classes exhibit polymorphism, the concept might lead the way to entirely new applications that operate based upon phase heterojunctions, that can be developed from a single product making use of straightforward as well as cost-effective manufacture processes.