HUST Team Unlocks High-Efficiency All-Perovskite Tandem Solar Cells

A research team from Huazhong University of Science and Technology (HUST) has announced a significant advancement in all-perovskite tandem solar cells. Utilizing quantitative Silvaco TCAD simulations, the team has meticulously clarified the fundamental physics governing the crucial tunnel junction, thereby establishing a definitive design rule to overcome long-standing efficiency limitations.

The Bottleneck: Unbalanced Charge Tunneling

While all-perovskite tandem solar cells boast a theoretical efficiency potential of around 45%, their practical performance has often been restricted by the limitations of their tunnel junction. This critical interlayer, typically structured as a SnO2/metal/PEDOT:PSS composite, serves to connect the top and bottom sub-cells.

The HUST researchers pinpointed the core challenge as a profound imbalance in charge tunneling. A key finding highlighted the disparity in effective mass: electrons in SnO2 possess an effective mass of approximately 0.2m₀, significantly lower than the approximately 4.8m₀ effective mass of holes in PEDOT:PSS.

This disparity results in the hole tunneling probability being four orders of magnitude lower than that of electrons, making hole transport the primary bottleneck within the tunnel junction.

The Breakthrough: Optimal Work Function Identified

To address this critical imbalance, the team rigorously investigated the pivotal role of the interlayer metal's work function (ΦM) in determining energy barriers at semiconductor interfaces. By systematically scanning ΦM across a range from 4.2 eV to 5.6 eV, the study precisely identified an optimal value of approximately 5.1 eV.

At this optimal work function:

• The barrier for holes at the HTL/metal interface is significantly minimized, reduced to approximately 0.2 eV.
• A moderate barrier of about 0.5 eV is judiciously maintained for electrons at the ETL/metal interface.
• This carefully balanced configuration powerfully facilitates efficient bidirectional tunneling.
• The equivalent series resistance of the tunnel junction is reduced to a remarkably low ~10⁻² Ω·cm².

Impact on Solar Technology

The study conclusively demonstrates that work function-driven band alignment is the central design principle for engineering high-performance tunnel junctions. These quantitative findings provide invaluable guidance for the selection of materials and alloys, pushing the development of all-perovskite tandem solar cells closer to their theoretical efficiency limits.

The research, titled "Tunnel junction simulation of all-perovskite tandem solar cells," was officially published in Frontiers of Optoelectronics on January 7, 2026.