Stable CsPb_1–xZn_xI₃ Colloidal Quantum Dots with Ultralow Density of Trap States for High-Performance Solar Cells

Abstract

All inorganic halide perovskites in the form of colloidal quantum dots (QDs) have come into people’s view as one of the potential materials for the high-efficiency solar cells; nevertheless, the high surface trap density and poor stability of QDs restrict the performance improvement and application. Here, we obtain colloidal inorganic perovskite CsPb1–x Zn x I3 QDs by the hot-injection synthesis process with the addition of ZnCl2. Synchrotron-based X-ray absorption fine structures demonstrate that the guest Zn2+ ions are doped into the CsPbI3 structure to improve the local ordering of the lattice of the perovskite, reducing the octahedral distortions. The increase of the Goldschmidt tolerance factor and the Pb–I bond energy also enhance the stability of the perovskite structure. Furthermore, the Cl– ions from ZnCl2 occupy the iodide vacancies of the perovskite to decrease the nonradiative recombination. The synergistic effect of doping and defect passivation makes for stable colloidal CsPb0.97Zn0.03I3 QDs with ultralow density of trap states. The champion solar cell based on the QDs shows a power conversion efficiency of 14.8% and a largely improved stability under ambient conditions.

All‐Inorganic CsPbI3 Quantum Dot Solar Cells with Efficiency over 16% by Defect Control

“…The decrease in particle size can be mainly attributed to the increase of I − in the reaction system, which suppressed the growth of QDs. [ 46,47 ] It is noted that an opposite result was observed in a previous report with use of ZnCl 2 as the dopant in preparation of CsPbI 3 QDs, [ 35 ] wherein with the increase of Zn content, the particle size of the corresponding QDs increased systematically. This difference clearly indicates that ZnCl 2 and ZnI 2 are significantly different in regulating the growth of the resulting CsPbI 3 QDs.…”

“…[ 15,16 ] The thermodynamic stability of α‐CsPbI 3 will be improved by reducing its size from bulk to nanoscale dimensions, owing to the enhanced total Gibbs free energy by the increased surface energy. [ 16 ] Since 2016, perovskite quantum dots solar cells (QDSCs) have attracted much research attention, [ 16–35 ] and the obtained PCEs quickly surpassed traditional QD‐based solar cells. [ 36–39 ] Swarnkar et al.…”

“…[ 44,45 ] There are many reports on regulating the defect states of CsPbI 3 QDs during the synthesis process. [ 20,35,43 ] However, few reports have paid attention to the formation of additional defect states during the post‐treatment and film fabrication processes for CsPbI 3 QDs. Therefore, to improve the performance of CsPbI 3 QDSCs, it is necessary to prepare CsPbI 3 QDs and QD films with low V I defect density.…”

“…In this work, we propose a simple strategy to reduce the V I defect states and enhance the stability of CsPbI 3 QDs simultaneously by anion/cation synergistic effect, thereby improving the efficiency and stability of CsPbI 3 QDSCs. Different from the literature report using ZnCl 2 as the dopant, [ 35 ] in our work, we used ZnI 2 as the dopant to synthesize Zn‐doped CsPbI 3 (Zn:CsPbI 3 ) QDs with the iodine‐rich surface. Experimental results demonstrated that the obtained Zn:CsPbI 3 QDs have higher PLQY and better stability compared to pristine CsPbI 3 QDs.…”

Efficient Thermally Activated Delayed Fluorescence from All‐Inorganic Cesium Zirconium Halide Perovskite Nanocrystals

“…The Bi 3+ 4f 7/2 can be fitted from the high‐resolution Bi4f XPS spectrum (Figure S16b), which locates at 159.1 eV featuring a doublet separation of 5.30 eV with Bi 3+ 4f 5/2 . The binding energies of Zr3d (Figure S16d) and Cl2p (Figure S16e) for the doped Cs 2 ZrCl 6 NCs shift to significantly lower energy levels in reference to the undoped ones, while those of Cs3d (Figure S16c) are almost unchanged, indicating the changed chemical environment of [ZrCl 6 ] 2− octahedra [31] . These results reveal Bi 3+ ions are doped into the lattices of Cs 2 ZrCl 6 NCs and occupy Zr 4+ sites.…”