Energy Level Modification with Carbon Dot Interlayers Enables Efficient Perovskite Solar Cells and Quantum Dot Based Light‐Emitting Diodes

Abstract

Controlling the transport and minimizing charge carrier trapping at interfaces is crucial for the performance of various optoelectronic devices. Here, how electronic properties of stable, abundant, and easy‐to‐synthesized carbon dots (CDs) are controlled via the surface chemistry through a chosen ratio of their precursors citric acid and ethylenediamine are demonstrated. This allows to adjust the work function of indium tin oxide (ITO) films over the broad range of 1.57 eV, through deposition of thin CD layers. CD modifiers with abundant amine groups reduce the ITO work function from 4.64 to 3.42 eV, while those with abundant carboxyl groups increase it to 4.99 eV. Using CDs to modify interfaces between metal oxide (SnO2 and ZnO) films and active layers of solar cells and light‐emitting diodes (LEDs) allows to significantly improve their performance. Power conversion efficiency of CH3NH3PbI3 perovskite solar cells increases from 17.3% to 19.5%; the external quantum efficiency of CsPbI3 perovskite quantum dot LEDs increases from 4.8% to 10.3%; and that of CdSe/ZnS quantum dot LEDs increases from 8.1% to 21.9%. As CD films are easily fabricated in air by solution processing, the approach paves the way to a simplified manufacturing of large‐area and low‐cost optoelectronic devices.

Methanol-induced fast CsBr release results in phase-pure CsPbBr3 perovskite nanoplatelets

“…Metal halide semiconductors with a perovskite crystal structure are famous for their excellent electrical and optical properties. [1][2][3][4][5] Showing high photoluminescence (PL) quantum yields (QYs), 6,7 an optimal range of band gap energy values and high defect tolerance, [8][9][10][11] the perovskite nanomaterials hold great promise for solar cell, 12 photodetector, 13 laser, 14,15 light-emitting diode (LED) and display applications. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Being free from the organic component, the all inorganic CsPbX 3 (X À stands for halide ions) perovskites are compositionally stable up to their melting points which are in excess of 460 C, 31 and thus have attracted enormous interest.…”

Multifunctional Charge Transporting Materials for Perovskite Light‐Emitting Diodes

“…Zheng et al incorporated carbon dots (CDs) onto a ZnO layer as an ETL and investigated the surface chemistry of the CDs by changing the precursor ratio of citric acid (CA) to ethylenediamine (EDA). [148] By adding a thin CD layer to the ETL, the work function of ITO could be adjusted over a broad range of 1.57 eV, showing a reduced ITO work function with abundant amine groups or increased values with many carboxyl groups on the CD surface. Because a thin CD layer can be easily prepared under ambient conditions via solution processing using water as a solvent, it is a good candidate for roll-to-roll large area production.…”

Emergence of Impurity-Doped Nanocrystal Light-Emitting Diodes

“…Compared with impurity-doped red and green PeLEDs, relatively little attention has been paid to impurity-doped blue PeLEDs. This may be because it is more difficult to synthesize high-performance blue perovskites together with the fact that it becomes harder to manipulate the device engineering due to the wide bandgap of blue emitters [ 305 , 306 , 307 , 308 ]. Encouragingly, B-site doping has been found to be a crucial way to fulfill high-performance blue PeLEDs [ 309 ].…”