Semiconductor photovoltaic structures are considered to be an important way to achieve clean energy because they can effectively convert solar energy into electrical energy. However, as early as 1961, the American scientist Shockley and the German scientist Kessel said that the efficiency of photovoltaic cells has theoretical limits due to inevitable losses. Among them, the spontaneous radiation loss due to photon absorption and re-radiation is the most critical, and this loss is proportional to the ratio of the spontaneous emission solid angle and the solid angle of sunlight. The solid angle of sunlight is only 6x10-5 spherical degrees, while the solid angle of spontaneous emission is 4Ï€ spherical degrees. This loss reduces the open circuit voltage of the traditional photovoltaic unit by more than 300 millivolts, greatly reducing the efficiency of the photovoltaic unit. In recent years, the emerging two-dimensional layered semiconductor material has become an energy-efficient structure that can be adjusted through thickness changes, and at the same time, through a unique van der Waals structure to achieve flexible heterogeneous integrated functional design and build efficient photovoltaic cells Current research hotspots. The key scientific issue is how to effectively control the spontaneous radiation loss, thereby improving the light absorption efficiency of the photovoltaic unit. In addition, it is not clear whether the efficiency limit of a two-dimensional material heterojunction photovoltaic unit and its advantages over traditional semiconductor photovoltaic structures. In response to the above problems, Liu Jiangtao, a professor at Guizhou University for Nationalities, and Wu Zhenhua, a researcher at the Institute of Microelectronics of the Chinese Academy of Sciences, carried out a series of theoretical studies and proposed the use of a single layer of molybdenum disulfide to construct a quasi-one-dimensional photonic crystal structure to achieve a photonic localized state. The matrix method proves that the light emission and absorption efficiency of the structure is improved by 2 ~ 3 orders of magnitude compared to the single layer of molybdenum disulfide [Scientific Reports, 7: 16391, (2017)], and proves that the two-dimensional photovoltaic unit can be realized through the metal microcavity Broad-spectrum enhanced absorption [Nanotechnology, 29: 14401 (2018)]. Recently, the joint research team proposed a new photovoltaic unit design scheme that combines a two-dimensional material heterojunction with a decoupling metal microcavity (as shown in the figure). This scheme greatly enhances the light absorption of the two-dimensional heterogeneous photovoltaic unit, and effectively reduces the spontaneous emission solid angle and the ratio of the spontaneous emission solid angle and the solid angle of sunlight, thereby reducing the loss caused by photon absorption and re-radiation. Theoretical calculations prove that the absorption efficiency limit of the new photovoltaic unit is about 1.1X times that of traditional photovoltaic devices. On this basis, the team further proposed a solution that is optimized by a common light focusing system that is easy to integrate. The optimized absorption efficiency can reach the performance level of the traditional photovoltaic unit under the assumption of perfect focusing theory. Since the spontaneous radiation loss increases with the thickness of the photovoltaic unit, the research based on the design of two-dimensional materials is currently the best solution towards the ultimate thickness. In the future, after the technology is mature, the new two-dimensional photovoltaic unit is expected to replace the traditional semiconductor photovoltaic unit, and has broad application prospects. This research work was recently published in Phys.Rev.Appl., 12: 034023, (2019). 2021 Coolest Design Solar 3D Acrylic Lawn Light Quality 3PCS LED Solar Garden Lamp with Light Sensor Waterproof Ipx5 Garden Lamp 3D Solar Lawn Light,LED Solar Garden Lamp,Solar Garden Lamp Dongguan XINYUDA Technology Co., Ltd. , https://www.gdxige.com
Schematic diagram of a new type of two-dimensional heterostructure photovoltaic unit and reference benchmark for absorption efficiency