Synthesis of N,S-Doped Carbon Quantum Dots for Use in Organic Solar Cells as the ZnO Modifier To Eliminate the Light-Soaking Effect.
Zinc oxide (ZnO) is one of the most extensively used electron-transporting layers (ETLs) in organic solar cells. However, owing to numerous surface defects and mismatched energy bands with the photoactive layer, light-soaking process is usually required to achieve a high device performance for the ZnO-based cells. Herein, we reported the synthesis of N,S-doped carbon quantum dots (N,S-CQDs) by a simple hydrothermal treatment using ascorbic acid and ammonium persulfate as reagents. As characterized by high-resolution transmission electron microscopy and X-ray diffraction, the synthesized CQDs were found to be 2-7 nm in dimensions, having a graphite-structured core and amorphous carbon on the shell. Fourier transform infrared and X-ray photoelectron spectroscopy analyses confirmed that these CQDs are highly nitrogen- and sulfur-doped, which leads to efficient (with a quantum yield of 33%) downconversion and excitation-dependent photoluminescence character. Application of these N,S-CQDs as surface modifier for ZnO layer in inverted organic solar cells was investigated. Results indicate that the cells with N,S-CQDs-decorated ZnO ETL showed higher power conversion efficiency without S-shaped kink in the current density-voltage curves. The performance improvement and the elimination of light-soaking effect for ZnO:N,S-CQDs cells are attributed to the ZnO surface defect passivation by N,S-CQDs, as confirmed by fluorescence spectroscopy and scanning Kelvin probe microscopy. The cells with N,S-CQDs-modified ZnO ETL showed a high power conversion efficiency of 9.31%, which is higher than the reference ZnO cells. The current work provides a feasible way to achieve shell element-doped CQDs for specific application in organic electronic devices.
['Wang|Yaling|Y|', 'Yan|Lingpeng|L|', 'Ji|Guoqi|G|', 'Wang|Cheng|C|', 'Gu|Huimin|H|', 'Luo|Qun|Q|http://orcid.org/0000-0002-7527-460X', 'Chen|Qi|Q|http://orcid.org/0000-0001-7721-8452', 'Chen|Liwei|L|', 'Yang|Yongzhen|Y|http://orcid.org/0000-0003-0566-4802', 'Ma|Chang-Qi|CQ|http://orcid.org/0000-0002-9293-5027', 'Liu|Xuguang|X|']
N,S-doped carbon quantum dots organic solar cells ZnO light-soaking effect surface passivation