Achieving rapid transport of photogenerated carriers and efficient separation in physical space is crucial for creating high-performance photovoltaic devices. This necessitates that carriers exhibit high mobility and low recombination rates within the light absorption layer, as well as effective separation and transport at the interface between the light absorption layer and the electron/hole transport layers, which significantly impacts device performance. Researchers have successfully fabricated high-efficiency lead halide perovskite polycrystalline films with grain sizes close to the micron scale. These films demonstrate an effective diffusion length for photogenerated carriers that surpasses the film's thickness, allowing for quick transport at very low recombination rates. The progress in perovskite film preparation technology has greatly enhanced device performance, making the properties of the device interface the primary factor limiting the advancement 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, thereby improving the separation and subsequent transport efficiency of photogenerated carriers. However, due to the vulnerability of interface modification materials to damage during subsequent perovskite film fabrication processes, passivation modifications of the buried interface (the lower interface, i.e., the perovskite light absorption layer/electron transport layer interface) remain in the developmental stage.
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, among others, to develop a method for reconstructing the buried interface energy level structure of devices. This method is based on the self-diffusion doping process and can efficiently separate interfacial photogenerated carriers while passivating the interface defects of the device. On August 25, the related research results 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 related patents were applied for.
The researchers introduced an amino acid derivative, L-aspartate potassium (PL-A), at the interface between the perovskite film and the electron transport layer of tin dioxide (SnO2) to regulate the properties of the device’s buried interface. The study found that the carboxyl group (-COO-) on PL-A can interact with SnO2 to passivate the surface defects of SnO2; simultaneously, the amino group (-NH2) on PL-A undergoes a coordination reaction with PbI2, passivating the lower surface defects of the perovskite film (Figure 1). Under these actions, the non-radiative recombination of photogenerated carriers at the perovskite film/electron transport layer interface is suppressed. Further analysis revealed that the potassium ions from PL-A can diffuse into the perovskite film and form gradient doping (Fig. 2a-f), thus optimizing the energy level structure on the perovskite side of the interface (Fig. 2g-h) and promoting carrier transmission within the film. The calculated results indicate that PL-A at the interface forms an oriented distribution (Fig. 1e), generating an additional dipole that regulates the work function of SnO2, thereby reducing the open-circuit voltage (Voc) loss. With the coordinated optimization of these functions, the performance of the device was significantly improved. Combined with the team's earlier research on optimizing the top device interface performance (*Nano Energy* 2021, 90, 106537), the photoelectric energy conversion efficiency reached up to 23.74% (Figure 3). Additionally, this interface modification process also showed good 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.
[Figure descriptions omitted for brevity but could be expanded further if needed.]
The work highlights a promising approach to overcoming key challenges in perovskite solar cell development, offering new avenues for future research and applications in renewable energy technologies.
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