Longi, a Chinese solar module manufacturer, has achieved a power conversion efficiency of 34.85% for a two-terminal tandem perovskite solar cell, setting a new world record for this cell type. The result was certified by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL).

This milestone surpasses Longi’s previous record of 34.6% for a similar cell configuration, announced in September. The company had published a scientific paper detailing the cell’s design, initially revealed in November 2023. The new efficiency exceeds the single-junction Shockley-Queisser limit of 33.7% for double-junction tandem solar cells, marking a significant advancement.

In September, Longi’s research team described the cell’s bilayer interface passivation strategy, which enhances electron transport and hole blocking. They explained: “Thicker LiF layer may help improve the passivation, but come with a considerable undesirable resistive loss. Nevertheless, EDAI molecule can chemically passivate the unpassivated areas that are not contacted by the LiF layer, forming nanoscale localized contacts at perovskite/C60 interface, which can provide an optimal tradeoff between passivation and charge extraction.”

The team utilized a patented technology for silicon heterojunction solar cells with an asymmetric textured surface. They noted: “The front surface of this silicon cell has a fine textured surface, facilitating the solution-based preparation of perovskite film, while the rear surface of the silicon cell uses a standard large size textured surface to achieve better passivation and infrared spectral response.” This design improved structural coupling between the perovskite top cell and the crystalline silicon bottom cell.

The LiF/EDAI bilayer increased the cell’s open-circuit voltage to 1.97 V and fill factor to 83.0%, reducing interfacial recombination and enhancing charge extraction at the electron transport layer interface. These improvements were critical to achieving the record efficiency.

The research was supported by Suzhou University, Huaneng Clean Energy Research Institute, and the Hong Kong Polytechnic University, contributing to the project’s success. Longi’s breakthrough underscores its commitment to advancing solar technology, supporting global efforts to improve renewable energy efficiency.

by pv magazine