A research team from Shanghai Institute of Optics and Fine Mechanics (SIOM) of Chinese Academy of Sciences (CAS) collaborated with Huazhong University of Science and Technology (HUST) has succeeded in discovered the ultrafast hot electron extraction mechanism in CdS/Sb₂Se₃ heterojunctions prepared for low-toxic and low-cost thin film solar cells. This study has been published in ACS Energy Letters on April 9, 2021.

With the shortage of fossil energy have been a public human being's problem, recent years have witnessed a surge of researches pertaining to the improvement of the photoelectric conversion efficiency of solar cells. At the same time, the cutting-edge researches on low-cost and high-efficiency solar cells in China will also provide an important theoretical and experimental basis for the overall goal of China's carbon-neutral target for 2060.

The efficiency of antimony selenide (Sb₂Se₃) solar cells has been improved from <2% to >10% within only seven years, but fundamental properties at the heterojunction interface such as charge carrier transfer and trap state localizing process have not been studied yet. Understanding and reducing all the possible charge carrier loss channels before the recombination is essential for achieving the ultimate thermodynamically limited conversion efficiency. In this work, time-resolved terahertz spectroscopy has been used to study the kinetics of carrier extraction and charge separation, and tin oxide (SnO₂) has been used as an electron transport layer to manipulate the ultrafast electron extraction process. Two different extraction mechanisms of photo-generated carriers have been revealed in CdS/Sb₂Se₃ and SnO₂/Sb₂Se₃. The carrier trapping process within ~20ps in the CdS/Sb₂Se₃ is suppressed by the hot electron extraction process in SnO₂/Sb₂Se₃. In contrast, the hot electron extraction at SnO₂/Sb₂Se₃ interface is nearly an order of magnitude faster than the trapping process, which can effectively suppress the photoinduced carrier trapping process. These results are expected to provide new insight for the film growth and device design to further improve the efficiency of tellurium selenide solar cells.

This work was supported by the National Natural Science Foundation of China, the Strategic Priority Research Program of the Chinese Academy of Sciences, and the Program of Shanghai Academic/Technology Research Leader.

Figure: the time-resolved terahertz spectrum of Sb₂Se₃ is different from the relaxation path of hot carriers when only Sb₂Se₃ is illuminated. (Image by SIOM)

Article website:
https://doi.org/10.1021/acsenergylett.0c02660

Contact:
WU Xiufeng
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: xfwu@siom.ac.cn
Web: http://english.siom.cas.cn/