Research Progress of Photovoltaic National Laboratory Thin Film Solar Cell

On March 27th, Nature Energy published a new research report on the stable and non-toxic selenium tellurium thin-film solar cells issued by Prof. Tang Jiang's team at the National Laboratory of Optoelectronics. The paper was entitled "Stable 6%- Efficient Sb2Se3 solar cells with a ZnO buffer layer”.

Under the energy crisis and environmental pressure, a wave of new energy research has been launched worldwide, and solar energy applications have won the top spot. Thin-film solar cells have the characteristics of low production cost, low light and high-temperature power generation performance, and light and flexible properties, and have a competitive advantage over silicon-based solar cells in photovoltaic building integration and mobile power supply. The most successful thin film solar cell on the market today is cadmium telluride (CdTe) battery, but Cd is extremely toxic and Te is very scarce.

Professor Tang Jiang's research group has been focusing on the research of a new type of selenide-doped (Sb2Se3) thin film solar cell. The research group has successively been in Advanced Energy Materials, ACS Applied Materials and Interface, Applied Physics Letters, and Progress in Photovoltaics. In addition, Nature Photonics published a paper demonstrating that the selenium telluride has the core advantages of simple cadmium telluride-based materials, rapid preparation, and excellent photoelectric properties, but the selenium tellurium itself is non-toxic and elemental rich. High and promising to become a "green cadmium telluride" has great potential for development.

In this study, zinc oxide (ZnO) was used as a buffer layer for the selenide antimony thin-film solar cell instead of the previously used cadmium sulfide (CdS). The material itself and the preparation method were both green and economical. Since the selenide tellurium is a one-dimensional chain material, ie, the molecular chain of (Sb4Se6)n is deposited in two directions by van der Waals force, similar to the one-dimensional polymer of the crystal, so the film orientation is very important, and the device performance is Great influence.

It was found that randomly oriented zinc oxide can induce [221]-oriented gallium selenide thin films, while [001] oriented zinc oxide induces [120] oriented selenide germanium thin films; the orientation is highly correlated with the orientation of gallium selenide thin films. . The atomic model analysis of the interface shows that more (100) planes are exposed on the surface of the randomly oriented zinc oxide, which facilitates bonding with the subsequently grown selenium telluride, reduces the total interface energy, and thus induces orientation induction. The device thus prepared had fewer interface defects and decreased composite loss. This was confirmed by both the biased external quantum efficiency spectrum and the open-circuit voltage at variable temperatures.

Through the series optimization of the zinc oxide film formation process and the back-end treatment of the selenium tellurium, the researchers finally achieved a 5.93% photoelectric conversion efficiency of the top lining structure (FTO/ZnO/Sb2Se3/Au) selenide thorium thin film solar cells, and Obtained Newport's third-party authority certification. More importantly, the solar cells thus prepared exhibit excellent stability under unencapsulated conditions and can experience dual 85 (temperature 85°C, humidity 85%), continuous maximum power point operation, strong ultraviolet light irradiation, and thermal shocks. With such harsh tests, the stability has basically reached the IEC61646 standard for thin-film solar cell applications. Compared to cadmium sulfide buffer layer, the stability of the device using zinc oxide buffer layer is significantly improved: the first-principles calculations show that the diffusion energy of Zn atoms in selenium telluride is larger than that of Cd atoms, and high angle dark field scanning transmission electron microscope ( The results of spatial elemental distribution under HADDF-STEM show that Cd diffuses near 50nm in yttrium selenide, while Zn diffusion is minimal, so the heterogeneous interface diffusion of ZnO/Sb2Se3 is small and the stability is high. The open-circuit voltage decay test of the monochromatic light also shows that the absorption of zinc oxide is small, and the damage of the gallium selenide by the photogenerated holes is suppressed. This study not only develops new ideas and methods for the regulation of one-dimensional chain material orientation, but also initially solves the last three points in the application of four key factors (efficiency, stability, low cost, and low toxicity) for solar cell applications. Big progress.

After the publication of the article, Dr. Supratik Guha from the American Materials Society (MRS) and the Society of Physics (APS) wrote the "Buffer against degradation" news & views in the same period of "Nature Energy" (Nature Energy). The dissertation article commented on “Tony and colleagues are significant milestones” in “Reduced toxicity and improved stability shown by Tang and colleagues”.

This research work has been supported by the National Key R&D Program, the Fund's Key R&D Plan Nurturing Project and the Youqing Project. PhD students Wang Liang, Li Kanghua and Chen Chao, postdoctoral Li Dengbing are the co-first authors of the thesis, and Professor Tang Jiang is the author of the paper. This work was also supported by Associate Professor Song Haisheng of Optoelectronic National Laboratory, Associate Professor Li Luying, Associate Professor Niu Guangda, Associate Professor Deng Huixiong of the Institute of Semiconductors of the Chinese Academy of Sciences and Professor Huang Feng of Sun Yat-sen University.

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