A team led by Professor Xu Jixian from the University of Science and Technology of China has introduced a novel structure and groundbreaking solution called PIC (porous insulator contact) to address the longstanding "passivation-transmission" dilemma in perovskite solar cells. Through rigorous theoretical modeling and experimentation, the research team outlined the design principles and concept validation for the PIC solution, setting a world record for steady-state certified efficiency in pin-type tandem solar cells. The PIC approach demonstrates broad applicability across various substrates and perovskite compositions. On February 17, the study titled "Reducing nonradiative recombination in perovskite solar cells through a porous insulator contact" was published in *Science*.
The "passivation-transmission" conflict is a recurring issue in optoelectronic devices like solar cells, LEDs, photodetectors, and more. To minimize non-radiative recombination losses at the semiconductor surface, a passivation layer is typically applied to reduce defect density. However, these passivation materials often have low conductivity, and increasing their thickness enhances passivation but hampers current transmission. This forces ultra-thin passivation layers to be precisely controlled within nanometers, complicating mass production.
Perovskite solar cell technology has garnered significant interest recently due to its potential to offer low-cost, high-efficiency alternatives to traditional crystalline silicon solar cells. Challenges remain, particularly non-radiative recombination losses at heterojunction contacts, which limit performance. Current approaches struggle to balance passivation and current flow, necessitating innovative contact designs.
After extensive exploration, the research team developed the PIC contact structure. Unlike conventional passivation techniques, PIC employs a porous insulating layer about 100 nanometers thick, forcing carriers to pass through localized openings rather than relying on ultra-thin passivation layers. The team’s semiconductor device modeling revealed that the PIC structure's period must align with the perovskite carrier transport length. While similar to local contact technologies in crystalline silicon solar cells, PIC demands precision at the 100-nanometer scale due to perovskite’s shorter carrier diffusion lengths. Utilizing nanosheet size effects, researchers transitioned from a "layer + island" model to an "island" (Volmer-Weber) model, employing low-temperature, cost-effective solution-based methods to fabricate the nanostructures.
In pin-type tandem devices, the PIC scheme successfully reduced hole interface recombination speeds from approximately 60 cm/s to 10 cm/s, achieving a single-junction maximum efficiency of 25.5% (steady-state certified efficiency of 24.7%). This improvement applies to various perovskite compositions and bandgaps, showcasing PIC’s broad applicability. Additionally, the PIC structure improves perovskite film formation and crystallization quality on hydrophobic substrates, enhancing carrier lifetime—a critical step toward scalable manufacturing.
Notably, the PIC solution is versatile and can be adapted to other device architectures and interfaces. Simulation results suggest further optimization could unlock additional performance gains beyond the current experimental coverage. This work received support from organizations including the National Natural Science Foundation of China, the Ministry of Science and Technology, and international collaborators from the University of Colorado Boulder.
The accompanying figures illustrate the PIC design principles, fabrication process, and performance metrics. Figure 1 outlines PIC's device simulation and design. Figure 2 details how nanosheet size effects enable PIC realization. Figures 3 and 4 demonstrate PIC's effectiveness in inhibiting non-radiative recombination and verifying its performance in pin-type tandem devices.
This research represents a major advancement in perovskite solar cell technology, addressing long-standing challenges and paving the way for future innovations in clean energy solutions.
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