Achieving rapid transport of photogenerated carriers and efficient spatial separation is crucial for creating high-performance photovoltaic devices. This necessitates carriers having high mobility and low recombination rates within the light-absorbing layer, while their separation and subsequent transport at the interface between the light-absorption layer and the electron/hole transport layers play a decisive role in device functionality. Scientific researchers have successfully developed lead halide perovskite polycrystalline films with grain sizes close to the micron scale. These films exhibit an effective diffusion length for photogenerated carriers that surpasses the film's thickness, enabling fast transport at very low recombination rates. The advancements in perovskite film fabrication techniques have significantly boosted device performance, with the interface properties now becoming the primary limiting factor in the progress of perovskite solar cells.
For positive-structured perovskite solar cells, constructing two-dimensional/three-dimensional heterostructures on the perovskite film surface has been shown to effectively adjust the energy level structure at the top interface of the device, enhancing the separation and subsequent transport efficiency of photogenerated carriers. However, since the interface modification materials can be easily damaged during the subsequent perovskite film preparation process, passivation modifications of the buried interface (the lower interface, specifically the perovskite light-absorption layer/electron transport layer interface) remain in the developmental stages.
Recently, the Shenyang National Research Center for Materials Science, Institute of Metals, Chinese Academy of Sciences collaborated with Huaqiao University and the Swiss Federal Institute of Technology in Lausanne to develop a method for reconstructing the buried interface energy level structure of devices. This approach leverages the self-diffusion doping process, achieving both efficient separation of interfacial photogenerated carriers and passivation of device interface defects. On August 25, the relevant research findings were published in *Advanced Functional Materials* under the title "Robust Interfacial Modifier for Efficient Perovskite Solar Cells: Reconstruction of Energy Alignment at Buried Interface by Self-Diffusion of Dopants," and a patent application was filed.
Researchers introduced an amino acid derivative, L-aspartate potassium (PL-A), at the interface between the perovskite film and the tin dioxide (SnO2) electron transport layer to regulate the properties of the device’s buried interface. The study revealed that the carboxyl group (-COO-) on PL-A interacts with SnO2 to passivate its surface defects, while the amino group (-NH2) on PL-A coordinates with PbI2, passivating the lower surface defects of the perovskite film (Figure 1). Under these actions, non-radiative recombination of photogenerated carriers at the perovskite film/electron transport layer interface is suppressed. Further analysis showed that the potassium ions from PL-A diffuse into the perovskite film, forming gradient doping (Fig. 2a-f), which optimizes the energy level structure on the perovskite side of the interface (Fig. 2g-h) and promotes carrier transport within the film. Computational results indicate that PL-A at the interface forms an oriented distribution (Fig. 1e), generating an additional dipole that regulates the SnO2 work function, thus reducing open circuit voltage (Voc) losses. Through the coordinated optimization of these functions, device performance has seen a significant enhancement. Combined with the team’s earlier research on optimizing the top device interface (Nano Energy 2021, 90, 106537), the photoelectric energy conversion efficiency reached 23.74% (Figure 3). Additionally, this interface modification process demonstrates excellent performance improvement effects in the preparation of large-area devices.
This research was supported by the National Natural Science Foundation of China, the Liaoning Provincial Natural Science Foundation of China, and the Shenyang National Research Center for Materials Science.
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The research work represents a major breakthrough in the field of perovskite solar cells, offering a promising avenue for further exploration and practical applications.
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