Metal halide perovskites are receiving great attention as next-generation semi­conductors for solar energy conversion. Since the first demons­tration of 3.8 % efficiency in 2009, effi­ciencies have increased rapidly and state-of-the-art perovskite solar cells exhibit high efficiencies over 25 %, close to the record efficiencies of silicon photovoltaics. This fast growth during the last decade raises the question of whether perovskite solar cells will be able to reach the upper thermo­dynamic limit of photo­voltaic effi­ciency, which is known to be 34 % in single-junction semi­conductors. To approach this goal, it is theoretically known that the solar cell must not only be a good light absorber, but also be a good light emitter.

The researchers from the Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) at the TU Dresden noted the role of the photon recycling effect. When a photon is radiated inside re-absorbing semi­conductors such as perovskites, it can be re-absorbed by the emitter itself and generate a new photon via photo­luminescence. Such a process of recur­sively re-absorbing and re-emitting the photons is called photon recycling. While this phenomenon has been previously demons­trated by several research groups, its practical contri­bution to the efficiency of perovskite solar cells has been under extensive debate. Based on the devices prepared by the groups, the researchers discovered that photon recycling and light scattering effects greatly improve the light emission effi­ciency by a factor of ~ 5, signi­ficantly improving the photo­voltage of perovskite solar cells.

Their work reveals the practical benefits of photon recycling in perovskite solar cells. “Perovs­kites are already good absorbers. Now it’s time to improve their light-emitting ability, to even further increase their already high power conversion efficiencies”, says Changsoon Cho, who led the work as a Humboldt research fellow at IAPP. “Under­standing photon recycling is a crucial step towards this direction.” The work predicts that the contribution of photon recycling, along with the suppression of various opto­electrical losses, will lead to a further increase in performance in the future. Using photon recycling, the upper limit for the effi­ciency of the perovskite solar cells is shown to rise from 29.2 % to 31.3 %.

“With the funda­mental insights regarding the role of photon recycling at hand, we have a unique possibility to further enhance the perovskite solar cell efficiency, thus offering this techno­logy ever brighter prospects to compete with the well-established silicon-based photo­voltaics”, adds Yana Vaynzof, Chair of Emerging Elec­tronic Technologies at the Institute of Applied Physics and the Center for Advancing Electronics Dresden (cfaed). Indeed, the improve­ments in the potential of perovskite solar cells motivate to further pursue the commerciali­zation of this techno­logy. “Our research shows the potential of the techno­logy, but much further effort in research and development is needed before the techno­logy can enter mass production”, says Karl Leo, head of the IAPP and European Inventor Award winner. (Source: TU Dresden)

Reference: C. Cho et al.: Effects of photon recycling and scattering in high-performance perovskite solar cells, Sci. Adv. 7, eabj1363 (2021); DOI: 10.1126/sciadv.abj1363

Link: Optoelectronics, Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP), Technical University Dresden, Dresden, Germany