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    SPECIAL TOPIC — Emerging photovoltaic materials and devices

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    Surface modulation of halide perovskite films for efficient and stable solar cells
    Qinxuan Dai(戴沁煊), Chao Luo(骆超), Xianjin Wang(王显进), Feng Gao(高峰), Xiaole Jiang(姜晓乐), and Qing Zhao(赵清)
    Chin. Phys. B, 2022, 31 (3): 037303.   DOI: 10.1088/1674-1056/ac1fe0
    Abstract117)   HTML1)    PDF (3510KB)(71)      
    As the main distribution place of deep-level defects and the entrance of water, the interface is critical to determining both the power conversion efficiency (PCE) and the stability of perovskite solar cells (PSCs). Suitable interface design can dramatically passivate interface defects and optimize energy level alignment for suppressing the nonradiative recombination and effectively extracting the photogenerated carriers towards higher PCE. Meanwhile, a proper interface design can also block the interface diffusion of ions for high operational stability. Therefore, interface modification is of great significance to make the PSCs more efficient and stable. Upon optimized material choices, the three-dimensional halide perovskite graded junction layer, low-dimensional halide perovskite interface layer and organic salt passivation layer have been constructed on perovskite films for superior PSCs, yet a systematic review of them is missing. Thus, a guide and summary of recent advances in modulating the perovskite films interface is necessary for the further development of more efficient interface modification.
    Applications and functions of rare-earth ions in perovskite solar cells
    Limin Cang(苍利民), Zongyao Qian(钱宗耀), Jinpei Wang(王金培), Libao Chen(陈利豹), Zhigang Wan(万志刚), Ke Yang(杨柯), Hui Zhang(张辉), and Yonghua Chen(陈永华)
    Chin. Phys. B, 2022, 31 (3): 038402.   DOI: 10.1088/1674-1056/ac373a
    Abstract144)   HTML0)    PDF (4879KB)(100)      
    The emerging perovskite solar cells have been recognized as one of the most promising new-generation photovoltaic technologies owing to their potential of high efficiency and low production cost. However, the current perovskite solar cells suffer from some obstacles such as non-radiative charge recombination, mismatched absorption, light induced degradation for the further improvement of the power conversion efficiency and operational stability towards practical application. The rare-earth elements have been recently employed to effectively overcome these drawbacks according to their unique photophysical properties. Herein, the recent progress of the application of rare-earth ions and their functions in perovskite solar cells were systematically reviewed. As it was revealed that the rare-earth ions can be coupled with both charge transport metal oxides and photosensitive perovskites to regulate the thin film formation, and the rare-earth ions are embedded either substitutionally into the crystal lattices to adjust the optoelectronic properties and phase structure, or interstitially at grain boundaries and surface for effective defect passivation. In addition, the reversible oxidation and reduction potential of rare-earth ions can prevent the reduction and oxidation of the targeted materials. Moreover, owing to the presence of numerous energetic transition orbits, the rare-earth elements can convert low-energy infrared photons or high-energy ultraviolet photons into perovskite responsive visible light, to extend spectral response range and avoid high-energy light damage. Therefore, the incorporation of rare-earth elements into the perovskite solar cells have demonstrated promising potentials to simultaneously boost the device efficiency and stability.
    High-throughput computational material screening of the cycloalkane-based two-dimensional Dion—Jacobson halide perovskites for optoelectronics
    Guoqi Zhao(赵国琪), Jiahao Xie(颉家豪), Kun Zhou(周琨), Bangyu Xing(邢邦昱), Xinjiang Wang(王新江), Fuyu Tian(田伏钰), Xin He(贺欣), and Lijun Zhang(张立军)
    Chin. Phys. B, 2022, 31 (3): 037104.   DOI: 10.1088/1674-1056/ac4036
    Abstract156)   HTML0)    PDF (3192KB)(50)      
    Two-dimensional (2D) layered perovskites have emerged as potential alternates to traditional three-dimensional (3D) analogs to solve the stability issue of perovskite solar cells. In recent years, many efforts have been spent on manipulating the interlayer organic spacing cation to improve the photovoltaic properties of Dion—Jacobson (DJ) perovskites. In this work, a serious of cycloalkane (CA) molecules were selected as the organic spacing cation in 2D DJ perovskites, which can widely manipulate the optoelectronic properties of the DJ perovskites. The underlying relationship between the CA interlayer molecules and the crystal structures, thermodynamic stabilities, and electronic properties of 58 DJ perovskites has been investigated by using automatic high-throughput workflow cooperated with density-functional (DFT) calculations. We found that these CA-based DJ perovskites are all thermodynamic stable. The sizes of the cycloalkane molecules can influence the degree of inorganic framework distortion and further tune the bandgaps with a wide range of 0.9—2.1 eV. These findings indicate the cycloalkane molecules are suitable as spacing cation in 2D DJ perovskites and provide a useful guidance in designing novel 2D DJ perovskites for optoelectronic applications.
    An n—n type heterojunction enabling highly efficientcarrier separation in inorganic solar cells
    Gang Li(李刚), Yuqian Huang(黄玉茜), Rongfeng Tang(唐荣风), Bo Che(车波), Peng Xiao(肖鹏), Weitao Lian(连伟涛), Changfei Zhu(朱长飞), and Tao Chen(陈涛)
    Chin. Phys. B, 2022, 31 (3): 038803.   DOI: 10.1088/1674-1056/ac4022
    Abstract95)   HTML0)    PDF (1002KB)(41)      
    Carrier separation in a solar cell usually relies on the p—n junction. Here we show that an n—n type inorganic semiconductor heterojunction is also able to separate the exciton for efficient solar cell applications. The n—n type heterojunction was formed by hydrothermal deposition of Sb2(S,Se)3 and thermal evaporation of Sb2Se3. We found that the n—n junction is able to enhance the carrier separation by the formation of an electric field, reduce the interfacial recombination and generate optimized band alignment. The device based on this n—n junction shows 2.89% net efficiency improvement to 7.75% when compared with the device consisted of semiconductor absorber—metal contact. The study in the n—n type solar cell is expected to bring about more versatile materials utility, new interfacial engineering strategy and fundamental findings in the photovoltaic energy conversion process.
    Reveal the large open-circuit voltage deficit of all-inorganicCsPbIBr2 perovskite solar cells
    Ying Hu(胡颖), Jiaping Wang(王家平), Peng Zhao(赵鹏), Zhenhua Lin(林珍华), Siyu Zhang(张思玉), Jie Su(苏杰), Miao Zhang(张苗), Jincheng Zhang(张进成), Jingjing Chang(常晶晶), and Yue Hao(郝跃)
    Chin. Phys. B, 2022, 31 (3): 038804.   DOI: 10.1088/1674-1056/ac464b
    Abstract122)   HTML1)    PDF (1390KB)(38)      
    Due to excellent thermal stability and optoelectronic properties, all-inorganic perovskite is one of the promising candidates to solve the thermal decomposition problem of conventional organic—inorganic hybrid perovskite solar cells (PSCs), but the larger voltage loss (Vloss) cannot be ignored, especially CsPbIBr2, which limits the improvement of efficiency. To reduce Vloss, one promising solution is the modification of the energy level alignment between the perovskite layer and adjacent charge transport layer (CTL), which can facilitate charge extraction and reduce carrier recombination rate at the perovskite/CTL interface. Therefore, the key issues of minimum Vloss and high efficiency of CsPbIBr2-based PSCs were studied in terms of the perovskite layer thickness, the effects of band offset of the CTL/perovskite layer, the doping concentration of the CTL, and the electrode work function in this study based on device simulations. The open-circuit voltage (Voc) is increased from 1.37 V to 1.52 V by replacing SnO2 with ZnO as the electron transport layer (ETL) due to more matching conduction band with the CsPbIBr2 layer.