The increasing energy and environmental crisis urges people to seek green and renewable new energy forms. Solar cells can directly convert the continuous sunlight into electric energy, which is an ideal renewable energy. In recent years, the energy conversion efficiency of perovskite solar cells has been increasing. The certified efficiency has exceeded 25.2%, which has reached or even exceeded the requirements of industrialization. In addition, its low preparation cost and flexible preparation methods have attracted extensive attention. However, the defects of stability still need to be solved to meet the needs of commercialization. Although all inorganic perovskite solar cells are expected to fundamentally solve the thermal instability of organic-inorganic hybrid perovskite solar cells, the further development is still restricted by the large loss of open circuit voltage (VOC) and the performance degradation caused by the defects of large-area film forming process.
Recently, Ma Yaohua's team of Jinan University and Shenzhen advanced technology research institute of Chinese Academy of sciences have made progress in the research of high-efficiency inorganic cspbi2br perovskite solar cells and modules again. They modulate the C60 electron transport layer by the way of tpfpb and LiClO4 double doping, which greatly reduces the open circuit of solar cell devices Voltage (VOC) loss, and the solar cell module based on inorganic perovskite material is reported for the first time through the self-developed quasi curved surface thermal radiation heating film preparation method, the efficiency is more than 12%.
Due to the electron absorption properties of tpfpb dopant molecules of Lewis acid (Fig. 1a), the nuclear shielding of electrons in C60 molecules is weakened, thus the LUMO energy level of C60 molecules is reduced (Fig. 1E), the conduction band energy difference between ZnO and C60 is increased, the driving force of electronic drift at the interface is enhanced, and the injection of electrons is enhanced (Fig. 1F).
Figure 1. Interaction between C60 and tpfpb
The VOC of the inverted inorganic cspbi2br perovskite solar cell device is increased by more than 100 mV with the incorporation of tpfpb (Fig. 2a), and the energy conversion efficiency is more than 15% (Fig. 2b), but at the same time, a more serious hysteresis effect is introduced, which results in the phenomenon that the stable output power of the device increases first and then decreases continuously (Fig. 2D).
Figure 2. Photovoltaic performance of tpfpb doped device
It is found that the addition of tpfpb affects the π electron jump transmission between adjacent C60 molecules, which reduces the electron mobility and conductivity of the system, and increases the hysteresis effect of the battery devices. Therefore, lithium salt (LiClO4), which is not easy to absorb moisture and deliquesce, is further used for doping to enhance the electronic mobility and conductivity of the film (Figure 3).
Figure 3. C-AFM diagram and current distribution statistics: a) blank sample; b) tpfpb doped sample; c) double doped sample
A small amount of LiClO4 doping can not only further improve the device efficiency, but also significantly reduce the hysteresis effect. Finally, the inverted inorganic cspbi2br perovskite solar cell based on the double doped C60 electron transport layer has achieved 15.19% energy conversion efficiency in a small area of 0.09 cm2 (Figure 4b), and 1.0% in a large area 14.44% efficiency has been achieved on cm2 (Fig. 4D), which is the highest energy conversion efficiency reported on 1.0 cm2 based on cspbi2br perovskite absorption layer.
Figure 4. Photovoltaic performance of the solar cell corresponding to the double doped C60 electron transport layer in different areas
Further work, the solar cell module based on inorganic perovskite material is reported for the first time. Considering the heat radiation heating method used in the previous work, its application in the preparation of thin films on large-area substrates will cause the low-temperature phase transition process in the center region of the substrate to lag significantly behind the edge region (Fig. 5B1), resulting in the over crystallization of the edge region and phase separation. In this work, through the self-developed quasi curved surface thermal radiation heating method, i.e. introducing a curved glass directly under the substrate (Fig. 5a), to improve the temperature of the central area, so as to achieve the goal of synchronous phase transition between the central area and the edge area. Finally, based on the substrate size of 5 × 5 cm2, the solar cell module based on inorganic perovskite material (10.92) is reported for the first time And the efficiency is as high as 12.19%.
Figure 5. Schematic diagram of preparation method and photovoltaic performance of inorganic perovskite solar module
Relevant research papers were published in advanced materials, a top journal in the field of materials science. Liu Chong, Ph.D. student, is the first author, and Professor Mai Yaohua and Yang Yuzhao, associate researcher, are the co correspondents.
The research was supported by national key R & D projects (2018yfb1500103, 2016yfa0201001), Hebei University high level talents scientific research project (gcc2014013), and Guangdong Province high level university construction funds.
Original text (scan or long press QR code and go to the original page after identification): tailoring C60 for efficient organic cspbi2br perovskite solar cells and moduleschong Liu, Yuzhao Yang, Cuiling Zhang, Shaohang Wu, Liyu Wei, Fei Guo, gowri manohari arumugam, Jinlong Hu, Xingyuan Liu, Jie Lin, Ruud E. I. schropp, Yaohua maiadv. mater., 2019, 32, 1907361, DOI: 10.1002/adma.201907361
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