SCN-doped CsPbI₃ for Improving Stability and Photodetection Performance of Colloidal Quantum Dots

Abstract

Inorganic halide CsPbI3 perovskite colloidal quantum dots (QDs) possess remarkable potential in photovoltaics and light-emitting devices owing to their excellent optoelectronic performance. However, the poor stability of CsPbI3 limits its practical applications. The ionic radius of SCN − (217 pm) is comparable to that of I − (220 pm), whereas it is marginally larger than that of Br − (196 pm), which increases the Goldschmidt tolerance factor of CsPbI3 and improves its structural stability. Recent studies have shown that adding SCN − in the precursor solution can enhance the crystallinity and moisture resistance of perovskite film solar cells; however, the photoelectric properties of the material post SCN − doping remain unconfirmed. To date, it has not been clarified whether SCN − doping occurs solely on the perovskite surfaces, or if it advances within their structures. In this study, we synthesized inorganic perovskite CsPbI3 QDs via a hot-injection method. Pb(SCN)2 was added to the precursor for obtaining SCN − -doped CsPbI3 (SCN-CsPbI3). X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were conducted to demonstrate the doping of SCN − ions within the perovskite structures. XRD and TEM indicated a lattice expansion within the perovskite, stemming from the large steric hindrance of the SCN − ions, along with an enhancement in the lattice stability due to the strong bonding forces between SCN − and Pb 2+ . Through XPS, we confirmed the existence of the S peak, and further affirmed that the bonding energy between Pb 2+ and SCN − was stronger than that between Pb 2+ and I − . The space charge limited current and time-resolved photoluminescence results demonstrated a decrease in the trap density of the perovskite after being doped with SCN − ; therefore, the doping process mitigated the defects of QDs, thereby increasing their optical performance, and further enhanced the bonding energy of Pb-X and crystal quality of QDs, thereby improving the stability of perovskite structure. Therefore, the photoluminescence quantum yield (PLQY) of the SCN-CsPbI3 QDs exceeded 90%, which was significantly higher than that of pristine QDs (68%). The high PLQY indicates low trap density of QDs, which is attributed to a decrease in the defects. Furthermore, the SCN-CsPbI3 QDs exhibited remarkable water-resistance performance, while maintaining 85% of their initial photoluminescence intensity under water for 4 h, whereas the undoped samples suffered complete fluorescence loss due to the phase transformations caused by water molecules. The SCN-CsPbI3 QDs photodetector measurements demonstrated a broad band range of 400-700 nm, along with a responsivity of 90 mA•W −1 and detectivity exceeding 10 11 Jones, which were considerably higher than the corresponding values of the control device (responsivity: 60 mA•W −1 and detectivity: 10 10 Jones). Finally, extending the doping of SCN − into CsPbCl3 and CsPbBr3 QDs further enhanced their optical properties on a significant scale.

Efficient (>20 %) and Stable All‐Inorganic Cesium Lead Triiodide Solar Cell Enabled by Thiocyanate Molten Salts

“…Pb(SCN) 2 ,MASCN,F ASCN or GuaSCN (Gua: guanidinium)) has been demonstrated to have avery positive effect on regulating the Pb-I octahedron structure and film morphology. [40,[42][43][44][45] Recently,L ue tal. reported low-defect photoactive a-phase FAPbI 3 obtained at relatively low temperature by the assistance of MASCN vapor treatment.…”

Ligand exchange engineering of FAPbI3 perovskite quantum dots for solar cells

“…Due to the combined advantages of perovskites and quantum dots (QDs), such as low cost, solution processability, tunable bandgap energy (E g ) and high stability [1][2][3][4][5][6][7][8][9], perovskite QDs (PQDs) have received increasing attention for application in light-emitting diodes [10,11], photodetector [12][13][14], and solar cells [15,16]. Since the first PQD solar cells (PQDSCs) were successfully fabricated by Swarnkar et al in 2016 [17], with the material synthesis improvement [18][19][20], post-treatment of PQDs [21][22][23][24][25], and tuning device structure of solar cells [26][27][28][29], the performance of inorganic CsPbI 3 PQDSCs has considerably improved.…”

Antisolvent‐Assisted In Situ Cation Exchange of Perovskite Quantum Dots for Efficient Solar Cells

“…Solution-processed lead halide perovskite quantum dots (APbX 3 -PQDs, A = Cs + , methylammonium(MA + ) or formamidinium (FA + ); X = Cl − , Br − , or I − ) have drawn remarkable research interest for application in light-emitting diodes, [1] displays, [2] photodetectors, [3,4] and photovoltaics [5,6] due to their tunable bandgap energy (E g ), high photoluminescence quantum yields (PLQYs) and high stability. [7,8] In particular, lead iodide PQDs, such as CsPbI 3 or FAPbI 3 PQDs, with high light absorption coefficient and defect tolerance show high potential as photo active materials for next-generation solar cells.…”