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Fig. 1 Battery performance statistics (a) and current-voltage curve of optimal performance battery (b)
Figure 2 Current-voltage curve for model analysis (a) and model analysis calculation results (b, c, d)
Perovskite-type methylamine lead-iodine thin-film solar cells have attracted the attention of many scientific researchers because of their simple structure and low preparation cost.
Its photoelectric conversion efficiency has rapidly increased from 3.8% to more than 15% in the past 5 years, which is higher than the efficiency of amorphous silicon solar cells. It was selected by Science as one of the top ten scientific breakthroughs in 2013. With the further development and maturation of the battery technology, the battery efficiency is expected to exceed 20%, and it has a wide range of application prospects.
However, these high-efficiency batteries currently use relatively expensive organic molecules (such as Spiro-OMeTAD) as hole-transport materials, which greatly increase the cost of the battery, and the long-term stability of organic materials is worth further examination. Therefore, the development of high-efficiency perovskite-type thin-film solar cells without hole-transport materials has become one of the important research directions for this type of solar cells.
At present, the highest efficiency of reported perovskite thin-film solar cells without hole-transport materials has reached 8%, which is far lower than that of hole-based material-based perovskites. At the same time, there is still a debate on the mechanism of sensitization and heterojunction in the understanding of the working mechanism of this kind of solar cell.
Recently, Meng Qingbo, a researcher at the Institute of Physics of the Chinese Academy of Sciences/Beijing National Laboratory for Condensed Matter Physics (CPC) Clean Energy, improved the thin film deposition process, optimized the interface, and optimized the deposition of thin films without hole transport materials. The research of perovskite methylamine lead-iodine thin film solar cells has made important progress, with the battery efficiency breaking the first 10% and the open circuit voltage exceeding 900 mV (Figure 1).
For the first time, the single-heterojunction ideal diode model was used to systematically analyze the current-voltage characteristics of the battery (Figure 2). The results show that the current-voltage characteristics of this type of battery are in good agreement with the ideal model, which is a typical difference. Knot battery. The ideal factor A of the battery is between 1.85 and 1.93, indicating that the forward saturation current of the diode is mainly determined by the carrier recombination in the depletion region of the semiconductor, confirming for the first time the existence of the space charge region of the heterojunction.
At the same time, the series resistance of the battery and the forward saturation current of the diode are calculated. The results show that the series resistance of the battery and the forward saturation current of the diode are very small, and can be compared with the currently widely studied high-efficiency thin-film solar cells (such as Cu ( In, Ga)Se2, CdTe).
The impedance spectroscopy study further confirmed the accuracy of the ideal model analysis and obtained self-consistent calculation results, which directly proved that this type of battery is a heterojunction thin film solar cell. This conclusion has important guiding significance for the design and performance improvement of this kind of solar cell device.
The above findings were published in the latest issue of Applied Physics Letters (Appl. Phys. Lett. 104, 063901 (2014)). This work was supported by the Beijing Science and Technology Commission, the Ministry of Science and Technology, the National Natural Science Foundation of China, and the Chinese Academy of Sciences.
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