Perovskite solar cells have low cost and high efficiency, and are considered to be one of the most promising photovoltaic technologies for low-cost power generation. Now high-efficiency perovskite batteries generally use high-temperature sintered TiO2, which limits its application in flexible devices, and TiO2 can catalytically decompose perovskite under the action of light, seriously affecting the stability of the battery. At present, the efficiency of perovskite batteries has exceeded 23%, and stability issues have become the biggest bottleneck restricting its practical use.
Fang Junfeng, a researcher at the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, conducted in-depth research on the above issues and made new progress. First of all, for the problem of TiO2 requiring high temperature treatment, it is proposed to use polar fullerene (C60 pyrrolidine tris-acid, CPTA) to replace TiO2 as an electron transport material, and achieve a flexible perovskite battery efficiency> 17% . 2017, 7, 1701144); on this basis, PbI2 was further introduced as a nucleus at the interface, and nucleation was induced through the interface to optimize the growth of perovskite crystals, so that the device efficiency was increased to 20.2% (Adv. Funct. Mater. 2018 , 28, 1706317). At the same time, in the hole transport material, through the selection of the counter ion of the polyelectrolyte transport material (P3CT-N), the excessive aggregation of the polyelectrolyte is effectively suppressed, thereby improving the growth of the perovskite film at the interface The efficiency of Xiangpin perovskite cells is> 19%, and the efficiency of flexible devices is also 18%. The efficiency of large-area devices of 1cm * 1cm is> 15% (ACS Appl. Mater. Interfaces2017, 9, 31357; Advanced Science, 2018, 1800159).
On the basis of the above-mentioned high-efficiency pin perovskite battery, recently, the research team has made further progress in the stability of the perovskite battery. The continuous power output of the solar cell during actual power generation (light and load) is the core indicator to measure its practicality. In actual work, the ions inside the perovskite film will migrate directionally along the grain boundary, which is an important reason for the decline in the efficiency of the perovskite battery. In response to this problem, the team was the first to propose an in-situ cross-linking strategy to prepare perovskite batteries. Introduce a cross-linkable liquid organic small molecule (trimethylolpropane triacrylate, TMTA, Figure 1a) into the perovskite film. With the coordination of TMTA and PbI2 at the grain boundary, TMTA chemical "anchor" in the perovskite At the grain boundary, effectively passivate the grain boundary defects to achieve> 20% device efficiency; more importantly, after further heat treatment, TMTA can undergo in-situ cross-linking (Figure 1b), forming a stable cross-link at the grain boundary The polymer network (Figure 1c) increases the ion migration activation energy of the perovskite film from 0.21 eV to 0.48 eV, thereby effectively inhibiting the migration of ions along the grain boundaries. The perovskite battery based on this strategy can still maintain 80% of the initial efficiency after 400 hours of continuous maximum power output (load 0.84V) under full-spectrum standard sunlight (Figure 2). Compared with traditional perovskite batteries, Its working stability (T80) has been improved by 590 times. This work for the first time achieved the long-term working stability of methylamine lead-iodine perovskite batteries under standard sunlight (Xe lamp) and full spectrum (without filtering) for> 200 hours, which provided the preparation of efficient and stable perovskite batteries New ideas and methods. At the same time, the air stability (humidity 45% -60%) and thermal stability (85 ° C) of the perovskite battery have also been significantly improved, and the initial efficiency (or post burn-in efficiency) can still be maintained after> 1000 hours of aging more than 90 percent. Related work was published in Nature Communications (Nature Communications, 2018, 9, 3806) with the title of In-situ cross-linking strategy for efficient and operationally stable methylammoniun lead iodide solar cells. Fang Junfeng is the sole corresponding author of the paper, and Li Xiaodong is the first author.
The above work was supported by the CAS Frontier Science Key Research Program (CAS QYZDB-SSW-JSC047), the National Natural Science Foundation of China (51773213, 61474125), and the Postdoctoral Foundation (2017M610380).
Figure 1 (a) TMTA chemical structure; (b) TMTA heating cross-linking; (c) TMTA in-situ cross-linking schematic diagram in perovskite film
Figure 2 Continuous power output of perovskite battery based on in-situ cross-linking strategy (standard Xe lamp light source, full spectrum, constant 0.84V load)
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