CHEMICAL SCIENCE

Wuhan University has achieved a new breakthrough in high-speed coating technology of organic solar cells


On October 27, 2022, Beijing time, the team of Min Jie of Wuhan University published a new study entitled “High-Speed Sequential Deposition of Photoactive Layer for Organic Solar Cell Manufacturing Process” in the journal Nature Energy.

Through the introduction of stepwise coating technology, the research group realized the high-speed deposition of the active layer of organic solar cells and maintained the device performance of the active layer system, which showed the potential of high-throughput preparation of high-performance organic solar cells.

The corresponding author of the paper is Min Jie; The first author is Sun Rui.

Organic solar cells (OSCs) have attracted a lot of attention in the past two decades as a next-generation photovoltaic technology. Thanks to the rapid development of photovoltaic materials and in-depth understanding of topography control, interface and device engineering, single-junction OSCs can achieve energy conversion efficiency (PCE) of more than 19%. Despite the great success of OSCs in lab-scale device efficiency and robustness, as well as significant progress in low-cost material and device design and development, the urgent need for high-throughput fabrication solutions for OSC devices remains unaddressed and rarely reported. As we all know, to achieve the commercialization of organic solar cells, the golden triangle of PCE, stability and cost must be considered at the same time. However, in addition to the above parameters, the high-throughput fabrication of the device also reflects the application potential of emerging photovoltaic technologies.

Recently, Min Jie’s team at Wuhan University used the designed polymer: non-fullerene small molecule photovoltaic system PM6:T8 as the active layer material, and achieved high-speed preparation of PM6:T8 active layer by introducing scalable Doctor blade (DB) and Slot-die coating (SDC) technologies and adopting layer-by-layer (LbL) coating strategy to achieve high-speed preparation of PM6:T8 active layer and maintain its excellent device performance. In contrast, the use of traditional bulk heterojunction (BHJ) coating process at high speed will cause severe phase separation of the active layer and form a huge roughness, resulting in a sharp degradation of device performance.

High-speed coating of the active layer is achieved by LbL scraping technology.Based on the non-fullerene small molecule receptor T8 synthesized by the team, different solution processing techniques (Figure 1a, including BHJ spin coating process (BHJ-SC), BHJ scraping process (BHJ-DB) and LbL scraping process (LbL-DB)) were used, and the polymer PM6 was introduced as the donor material to optimize and prepare PM6:T8 devices with a PCE close to 18%. Furthermore, through the synergistic regulation of solution concentration and coating speed, the correlation between the efficiency trend of devices prepared by BHJ-DB and LbL-DB processes and the above processing parameters was systematically explored, and it was found that the high-speed coating of PM6:T8 active layer film could be achieved by using LbL-DB technology and its high device performance (PCE greater than 17.6%, Figure 1c). Conversely, the use of LbL-DB technology at the same processing speed will lead to serious phase separation of the active layer morphology, so the performance of PM6:T8 devices will be significantly reduced (Figure 1b). It is worth mentioning that it is found that the devices prepared by the LbL-DB process at speeds of 2.1 and 30.0 m/min show similar operational stability, and the photovoltaic performance of the relevant active layer is not sensitive to the humidity conditions of the processing environment.

Figure 1: (a) Schematic diagram of solution-based processable BHJ spin coating and scraping (BHJ-DB) and LbL scraping (LbL-DB) technologies; Device performance trends of active layer prepared by (b) BHJ-DB and (c) LbL-DB technologies under different concentration and coating speeds, respectively.

Versatility of high-speed LbL-DB processes.In addition to the above-mentioned use of chloroform solvent to coat the active layer, toluene, a non-halogenated solvent, is also used to construct related devices. Figures 2a and 2b show the photovoltaic performance of BHJ-DB and LbL-DB type devices prepared at different coating speeds, respectively. It can be seen that the efficiency of the LbL-DB type device processed by toluene still exceeds 17.15% at a coating speed of 30.0 m/min, which is far better than the LbL-DB type device (PCE is 13.32%). In addition, five non-fullerene photovoltaic systems (Figure 2c, including PM6:Y6, PM6:N3, PM6-Ir1:Y6, PM1:Y6 and PTQ10:Y6) were further introduced into this project to explore the correlation between the efficiency trend of the two processing processes and the coating speed, and the relevant results fully proved the versatility of the high-speed LbL-DB process.

Figure 2: Device properties vs. coating speed based on (a) BHJ-DB and (b) LbL-DB processes prepared from toluene solvents; (c) The device performance trends of five active layer systems (including PM6:Y6, PM6:N3, PM6-Ir1:Y6, PM1:Y6, PM1:Y6 and PTQ10:Y6) prepared by BHJ-DB and LbL-DB technologies under different concentration and coating speeds.

High-speed slit machining of OSC components and economic benefit analysis.As a proof of concept, the Min Jie team designed and developed a linkage layer-by-layer slit coating instrument for large-area device and component fabrication, as shown in Figure 3a. By balancing the processing parameters such as flow rate, substrate temperature, solution concentration and coating speed, the preparation of high-performance devices and components of PM6:T8 active layer at different coating speeds (area 1.0 and 7.5 cm2, respectively) was realized. Compared with BHJ slit coating (BHJ-SDC), LbL slit coating (LbL-SDC) can maintain the optimal performance of PM6:T8 system at high speed (Figure b), which also verifies the experimental data of the LbL-DB process mentioned above. In addition, using a bottom-up manufacturing cost model, Min Jie’s team further conducted a technical and economic benefit analysis of the BHJ and LbL processes. As shown in Figure 3c, LbL high-throughput fabrication technology can significantly reduce the lowest sustainable price (MSP) for PV module manufacturing in industrial production processes; The high-speed LbL technology with a line speed of 30.0 m/min can significantly reduce the MSP value (from 7.72 to 0.32 $/Wp with a difference of 7.40 $/Wp) compared to the conventional BHJ process with a line speed of 2.1 m/min.

Figure 3: (a) Schematic diagram of linkage type layer by layer slit coating instrument; (b) Component performance trends of active layers prepared by BHJ-SDC and LbL-SDC technologies under different concentration and coating speeds, respectively. (c) Economic benefit analysis based on BHJ and LbL process technology under different coating speeds.

This study provides a rational understanding of the design of active layer materials and the regulation of active layer morphology, reveals the defects of the traditional active layer coating process, and finds that the layer-by-layer coating process can achieve high-speed coating of active layers and maintain its high performance, which represents an important step towards high-speed, scalable and low-cost manufacturing of high-performance devices and components. This work is supported by the National Natural Science Foundation of China (52061135206) and the basic scientific research operation fund of the central universities. (Source: Web of Science)

Related Paper Information:https://doi.org/10.1038/s41560-022-01140-4



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