《Advanced Materials》Professor Zhan'ao Tan's team from Beijing University of Chemical Technology used Valinomycin (VM) to manage interfacial charged defects and achieved 24.06% efficient perovskite solar cells with enhanced efficiency and stability in Advanced Materials.
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Highlights
- The researchers inserted valinomycin (VM) at the interface between perovskite and electron transport layer as a buffer layer to eliminate interfacial charged defects in perovskite solar cells.
- Through theoretical calculations and experimental analysis, it is proved that the carbonyl, amino and ether groups in VM molecules can fix positive and negative charge defects and regulate interfacial energy level alignment.
- The inverted perovskite solar cells with VM buffer layer finally achieved a high power conversion efficiency of 24.06% and excellent long-term stability.
(The instruments used in this study are from Enlitech: Solar Simulator, and Quantum Efficiency Measurement System QE-R.)
Background
The unavoidable positively and negatively charged defects at the perovskite/electron transport layer interface in perovskite solar cells lead to severe surface recombination and unfavorable energy level alignment, limiting the efficiency. Inserting interlayers at this interface is an effective approach to eliminate interfacial defects. In this study, the macrocyclic molecule valinomycin (VM) with multiple active sites of carbonyl, amino and ether groups is employed as the buffer layer between perovskite and electron transport layer.
Results
Through a series of theoretical calculations and experimental analysis, it is demonstrated that the carbonyl (-C=O) and ether (-O-) groups in VM can immobilize the uncoordinated Pb2+ to manage the positive charge defects; the formed N-H⋯I hydrogen bonding can compensate the formamidine vacancies to eliminate the negative charge defects. In addition, the VM layer induces a favorable band bending at the perovskite/ETL interface, facilitating charge separation. Finally, the inverted perovskite solar cells with VM buffer layer achieve a high efficiency of 24.06% and excellent long-term thermal and ambient stability.
Methods
- The binding mechanics and electronic structure of VM molecules with defect models were calculated by density functional theory. The results show VM molecules can effectively fix positive and negative charge defects through active groups like carbonyl and amino.
- X-ray photoelectron spectroscopy, thermogravimetric analysis etc. were utilized to study the chemical composition and thermal stability of VM modified perovskite films, confirming significantly decreased defect state density by VM layer.
- Kelvin probe force microscopy was measured for perovskite solar cells with VM buffer layer, finding modulated energy level alignment at the perovskite/ETL interface.
- Inverted perovskite solar cells with VM buffer layer were prepared and their photoelectric conversion efficiency, thermal and long-term stability were tested. The results prove VM buffer layer can effectively improve the cell performance.
Conclusion
By introducing the VM molecule buffer layer with multiple active groups at perovskite/ETL interface, this work simultaneously managed interfacial charged defects and regulated energy level alignment, substantially boosting the efficiency and stability of perovskite solar cells. It provides a new strategy to design high-performance perovskite solar cells.
Figure S8. Calculated Eu for perovskite films (a) without and (b) with VM modification.
Figure S9. a) Electron mobility and b) hole mobility of the devices with or without VM
modification.
Figure S10. JSC versus light intensity plot.
Figure S18. J-V curves of devices with different concentrations of VM or without VM
modification.
Figure S20. XRD patterns of the perovskite films a) without or b) with VM modification
before and after aging 200 h under ambient environment (25 ± 5% RH). c) Diffraction
intensity ratio variation of PbI2 peak to perovskite (100) peak.
Keywords
QE-R、VM
