Unraveling the efficiency losses and improving methods in quantum dot-based infrared up-conversion photodetectors

Quantum dot-based up-conversion photodetector,in which an infrared photodiode(PD)and a quantum dot light-emitting diode(QLED)are back-to-back connected,is a promising candidate for low-cost infrared imaging.However,the huge efficiency losses caused by integrating the PD and QLED together hasn’t been studied sufficiently.This work revealed at least three origins for the efficiency losses.First,the PD unit and QLED unit usually didn’t work under optimal conditions at the same time.Second,the potential barriers and traps at the interconnection between PD and QLED units induced unfavorable carrier recombination.Third,much emitted visible light was lost due to the strong visible absorption in the PD unit.Based on the understandings on the loss mechanisms,the infrared up-conversion photodetectors were optimized and achieved a breakthrough photon-to-photon conversion efficiency of 6.9%.This study provided valuable guidance on how to optimize the way of integration for up-conversion photodetectors.

Improved blue quantum dot light-emitting diodes via chlorine passivated ZnO nanoparticle layer

In blue quantum dot light emitting diodes(QLEDs),electron injection is insufficient,which would degrade device efficiency and stability.Herein,we employ chlorine passivated ZnO nanoparticles as electron transport layer to facilitate electron injection into QDs effectively.Moreover,it suppresses exciton quenching at the QD/ZnO interface by blocking charge transfer channel.As a result,the maximum external quantum efficiency of blue QLED was increased from 2.55%to 4.60%,and the operation lifetime of blue QLED was nearly 4 times longer than that of the control device.Our work indicates that election injection plays an important role in blue QLED efficiency and stability.

High-brightness green InP-based QLEDs enabled by in-situ passivating core surface with zinc myristate

The performance of red InP and blue ZnTeSe-based quantum dots(QDs)and corresponding QD light emitting diodes(QLEDs)has already been improved significantly,whose external quantum efficiencies(EQEs)and luminances have exceeded 20%and 80000 cd m-2,respectively.However,the inferior performance of the green InP-based device hinders the commercialization of full-color Cd-free QLED technology.The ease of oxidation of the highly reactive InP cores leads to high non-radiative recombination and poor photoluminescence quantum yield(PL QY)of the InP-based core/shell QDs,limiting the performance of the relevant QLEDs.Here,we proposed a fluoride-free synthesis strategy to in-situ passivate the InP cores,in which zinc myristate reacted with phosphine dangling bonds to form Zn–P protective layer and protect InP cores from the water and oxygen in the environment.The resultant InP/ZnSe/ZnS core/shell QDs demonstrated a high PL QY of 91%.The corresponding green-emitting electroluminescence devices exhibited a maximum EQE of 12.74%,along with a luminance of over 175000 cd m^(-2)and a long T50@100 cd m^(-2)lifetime of over 20000 h.

Noise and detectivity limits in organic shortwave infrared photodiodes with low disorder

To achieve high detectivity in infrared detectors,it is critical to reduce the device noise.However,for non-crystalline semiconductors,an essential framework is missing to understand and predict the effects of disorder on the dark current.This report presents experimental and modeling studies on the noise current in exemplar organic bulk heterojunction photodiodes,with 10 donor-acceptor combinations spanning wavelength between 800 and 1600 nm.A significant reduction of the noise and higher detectivity were found in devices using non-fullerene acceptors(NFAs)in comparison to those using fullerene derivatives.The low noise in NFA blends was attributed to a sharp drop off in the distribution of bandtail states,as revealed by variable-temperature density-of-states measurements.Taking disorder into account,we developed a general physical model to explain the dependence of thermal noise on the effective bandgap and bandtail spread.The model provides theoretical targets for the maximum detectivity that can be obtained at different detection wavelengths in inherently disordered infrared photodiodes.