Light-trapping trick offers ultrathin solar cells with 28.2% high photocurrent

Researchers have created an ultra-thin perovskite solar cell with a checkerboard pattern that shields the perovskite layer from UV degradation.

The design developed by a team at the Nova University of Lisbon includes a luminescent down-shifting encapsulant, which enhances UV photon conversion and boosts overall efficiency.

“Through a combined optical and electrical modeling approach, this photonic structure can increase photocurrent and power conversion efficiency in ultrathin PSCs by 25.9 percent and 28.2 percent, respectively,” said the team in the study abstract.

The study also showed that over 94 percent of incoming UV radiation can be efficiently converted into the visible spectrum.

UV-protected PSCs

Perovskite-based materials have become a key focus in photovoltaic (PV) research due to their exceptional optoelectronic properties. These properties enable solar cells to achieve power conversion efficiencies (PCE) comparable to commercial silicon-based cells.

However, the lifespan of perovskite solar cells (PSCs) is affected by intrinsic and environmental factors, with UV degradation being a significant concern, especially in space applications where UV exposure is high.

To address this, researchers have developed strategies like using luminescent down-shifting (LDS) encapsulants that not only protect the cells but also convert UV photons into visible light, increasing external quantum efficiency (EQE).

Lanthanide-based materials, particularly Europium (Eu3+) and Terbium (Tb3+), have shown promise for UV-to-visible conversion, reducing UV-induced degradation and enhancing device stability.

Meanwhile, light-trapping (LT) techniques, such as grating structures, improve the optical path within the PSC, allowing thinner but more efficient absorbers.

Optimized light absorption

The team’s research introduces a new approach to improve the performance, UV resistance, and flexibility of perovskite solar cells (PSCs). The team used a combination of two innovative techniques: a special checkerboard design for light trapping (LT) and a material that converts UV light into visible light.

Initially, the checkerboard design was intended to enhance light absorption within the solar cells. They then paired it with a sophisticated coating composed of a substance modified with lanthanide, which helps shield the cells from damage by converting UV rays into visible light.

Even in cases when light strikes the cells at varied angles, the checkerboard-shaped LT design increases photocurrent by 25.9 percent. The ultrathin solar cells exhibit a 28 percent boost in efficiency, reaching a projected power conversion efficiency (PCE) of 24.1 percent with only a 250 nm perovskite layer.

Researchers highlight that despite possible fabrication faults, these LT structures exhibit great resilience, with performance fluctuating relatively little.

Additionally, the LDS coating, made from new material (t-U (5000)/Eu3+), enhances the solar cells’ stability without lowering their performance. It reduces damaging UV effects by 94 percent and slightly improves light absorption in the perovskite layer.

While the LDS coating has a greater impact on simpler PSC designs, the combination of LT and LDS works best for space applications . This approach improves efficiency and stability under high UV exposure and increases the power-to-weight ratio of solar panels.

According to researchers, by combining light trapping with luminescent downshifting layers, this work unravels a potential photonic solution to overcome UV degradation in PSCs while circumventing optical losses in ultrathin cells, thus improving both performance and stability.

The details of the team’s research were published in the journal Light .