Researchers are constantly looking to improve the performance of solar photovoltaic cells and materials. Now two teams from the Technical University of Dresden (TUD) have joined forces to demonstrate the formation of a “phase heterojunction” in a solar cell and it could be the start of a new era of efficiency in photovoltaics (PV).

In a typical silicon solar cell, a “p-n junction” is created when each side of the layered device is electrically doped. This creates an electric field that guides pairs of charge carriers from the sunlight absorbing side across the diode, generating current. Professor Vaynzof and her team from the Integrated Centre for Physics and Photonic Materials (IAPP) and the Centre for Advancing Electronics Dresden (cfaed) have instead figured out a way of exploiting a phenomenon called polymorphism – in a technique which involves interfacing two layers of the same perovskite material in different beta and gamma phases.

“The optical and electronic properties of caesium lead iodide in its beta and gamma phase are different from each other,” explains Vaynzof in the report in Nature. “By placing a gamma-perovskite on top of the beta-perovskite we were able to fabricate a phase heterojunction solar cell, that is significantly more efficient as compared to solar cells that are based on single phase perovskites.”

Importantly, the phase heterojunction remained stable during solar cell operation and even supressed ion migration in the solar cell absorber (solving a common problem with perovskites).

The phase differential was achieved by using two different fabrication processes for the top and the bottom layers. Vaynzof believes their new process will have a wider application beyond PV: “We hope that this novel concept combined with a simple fabrication route for phase heterojunctions will be applicable also to a variety of material systems in a range of electronic and optoelectronic devices” she says in a press release.