Angew：SNNU and CAS join hands to cooperate with Prof. Wanchun Xiang and others, Molecular Bridge on Buried Interface for Efficient and Stable Perovskite Solar Cells from 22.6% to 24.7%.

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Recently, Shaanxi Normal University’s Wan Chun team utilized the testing equipment of Light Flame Technology Company to develop perovskite solar cells with grafting of glutaraldehyde (GDA) at the SnO2/perovskite interface for molecular bridge optimization. This research combines advanced testing equipment and material development strategies to increase the cell conversion efficiency from 22.6% to 24.7% and significantly improve stability.

The molecular modifying agent glutaraldehyde (GDA) constructs molecular bridges at the buried SnO2/perovskite interface, resulting in excellent interfacial contacts.
The significant band alignment is achieved through strong interactions between GDA and SnO2. In addition, GDA can regulate the growth of perovskite crystals, producing perovskite films with increased grain size and no pinholes, with significantly reduced defect density.
The GDA-modified perovskite solar cells exhibit impressive open-circuit voltages close to 1.2 V and significantly improved fill factors, increasing the power conversion efficiency from 22.6% to 24.7%. Furthermore, GDA devices show better stability than control devices at maximum power point and 85°C thermal stress.

Background

Perovskite solar cells have attracted considerable attention due to their theoretically high conversion efficiency of 25%. However, the degradation of perovskite materials by temperature and humidity and ineffective charge transfer at the SnO2/perovskite interface lead to lower efficiencies than expected, hindering commercialization. Improving the conversion efficiency and long-term stability of perovskite solar cells is a current research hotspot. Leveraging advanced characterization equipment to develop high-performance perovskite materials and interface engineering technologies for simultaneous enhancements in efficiency and stability is the focus.

Results

The Wan Chun team at Shaanxi Normal University designed and developed the molecular material glutaraldehyde (GDA) to optimize the SnO2/perovskite interface. XRD analysis showed GDA regulates perovskite grain growth, producing high-quality perovskite films with increased grain size and reduced defect density. Additionally, GDA can modulate perovskite growth to form high-quality films, thus reducing defects and related non-radiative charge recombination. Consequently, GDA-modified PSCs exhibit an impressive VOC close to 1.2 V and champion efficiency of 24.70%, higher than the 22.60% of control devices and 24.22% of GAAc-modified PSCs. Hysteresis was also reduced. Finally, compared to control and GAAc-modified devices, GDA modification also significantly enhanced maximum power point (MPP) tracking and device stability under 85°C thermal stress. This work was published in Angewandte Chemie International Edition.

Methods

Equipment used:

This study used Light Flame Technology AAA class AM1.5G solar simulator and NREL-certified silicon reference cell SRC2020, as well as QE-R quantum efficiency measurement system.

Results and Discussion

Key Point 1: Molecular bridging between SnO2 and perovskite

The research team chose GDA as the interfacial modifier for perovskite for two reasons: First, GDA has high thermal stability and good solubility, providing stable support during interface formation and deposition. Second, the GDA molecule contains carboxyl and GA groups, enabling strong coordination with SnO2 and perovskite to bridge them, improving interfacial contact and facilitating charge transfer while reducing recombination.

Through experiments and DFT calculations, the research team demonstrated the chemical interactions between GDA and SnO2, mainly from the carboxyl groups in GDA binding with under-coordinated Sn4+ on the SnO2 surface. FTIR measurements also supported this, showing interactions between the GDA molecules and the SnO2 layer.

Key Point 2: GDA modification of the SnO2 layer

The research team characterized the effects of GDA on SnO2 layer morphology and roughness using top-view SEM and AFM. GDA modification resulted in a more uniform and continuous nanoparticle layer on the SnO2 surface with reduced roughness, benefiting nucleation and crystallization of the perovskite film for improved interfacial charge transfer.

UPS measurements revealed modified SnO2 band alignment with increased Fermi level after GDA modification, facilitating interfacial charge transfer. These results indicate GDA modification influenced the SnO2 band structure, improving PSC interface properties.

Key Point 3: Influence of underlayer modification on perovskite layer

The research team investigated perovskite layers deposited on GDA-modified and unmodified SnO2. SEM and XRD characterization showed GDA modification assisted in forming flatter, denser perovskite films with improved crystallinity, which is important for reducing charge defects and improving charge transfer efficiency.

Key Point 4: Influence of underlayer modification on perovskite film crystallization

In situ XRD measurements allowed the research team to study the impact of GDA modification on perovskite film crystallization. Results showed GDA modification influenced intermediate phase formation, causing lattice expansion. Additionally, GDA modification was found to affect perovskite film grain size and crystallization kinetics, further enhancing film quality.

Key Point 5: Device performance and stability

The research team fabricated GDA-modified and unmodified PSCs and evaluated their performance and stability. Results showed GDA-modified devices exhibited advantages in both photoelectric conversion efficiency (PCE) and stability. GDA modification helped suppress non-radiative recombination, improve carrier extraction efficiency, and reduce interfacial trap density, leading to enhanced PCE and stability.

Conclusion

This research leveraged advanced PV testing equipment to develop glutaraldehyde molecule material modification at the SnO2/perovskite interface, significantly improving perovskite solar cell efficiency and long-term stability. It demonstrates the enablement of material development through advanced characterization and proposes new design concepts for low-cost, high-efficiency, stable perovskite solar cell mass production. Cross-disciplinary collaboration across industry, academia and research is anticipated to accelerate practical application of efficient perovskite solar cells.