Colloidal Quantum Dot Solar Cell Band Alignment using Two-Step Ionic Doping

Abstract

Colloidal quantum dot (CQD) solar cells composed of ionic halide passivated active layers benefit from improved passivation and high carrier mobility because of short interparticle distance. However, non-ideal band alignment of the active layer limits the potential open-circuit voltage (V OC) produced by the solar cell. We initiated a suite of simulation-based studies of CQD solar cells and found a route to improved performance by increasing the degree of p-type behavior. Fluoride, while it is a p-type ionic ligand as desired, is incompatible with traditional ligand exchange processes. In prior studies, it has shown to etch the lead sulfide surface uncontrollably. Instead, we develop a multistep halide exchange method, in which the CQD active layer is doped with fluoride ions after ligand exchange. This new method prevents CQD surface etching without impeding charge transport, resulting in a statistically significant improvement in V OC, fill factor, and power conversion efficiency.

Controlled Crystal Plane Orientations in the ZnO Transport Layer Enable High‐Responsivity, Low‐Dark‐Current Infrared Photodetectors

“…[35] The oleic acid ligands were exchanged for halide ligands and an ink was made for spin coating, all using a published exchange and ink synthesis method. [36] Indium Tin Oxide (ITO) Cleaning: ITO glass substrates were cleaned in an ultrasonic bath of water, acetone, and isopropyl alcohol for 60, 30, and 30 min respectively. The substrates were fully dried before ETL deposition.…”

“…[ 35 ] The oleic acid ligands were exchanged for halide ligands and an ink was made for spin coating, all using a published exchange and ink synthesis method. [ 36 ]…”

Suppressing the Dark Current in Quantum Dot Infrared Photodetectors by Controlling Carrier Statistics

“…[26,27] Energy band engineering and doping strategies have also been developed between the n + n and the n-p junction to effectively dissociate the generated exciton by doping ZnO with K or Cs [28,29] and PbS with halide. [30] Postchemical treatment, [15,31] or surface passivation methods, [13,18] have been investigated to improve the carrier mobility and lifetime for efficient charge transport. To achieve efficient charge collection and improve the sensitivity, a buffer layer or interfacial layer between the electrode and charge transport layer has been examined.…”

Trap-Filling Magnetoconductance as an Initialization and Readout Mechanism of Triplet Exciton Spins

“…Figure shows the device layers and characteristics under normal operating conditions. PEDOT:PSS was chosen as an efficient hole injection layer, and a gold top contact was chosen, so that the Fermi level provides a small energetic barrier for hole transport but a large barrier for electron transport, making it a commonly chosen electrode for hole extraction. − The additional 150 nm of silver provides contact stability and reduces the possibility of shunting without altering the device electrical properties as outlined in the Supporting Information. The positive bias regime of the J – V curve resembles ideal space-charge limited current models, but an increasing slope–voltage relationship with increasing bias suggests nonideal behavior.…”