Improved Current Extraction from ZnO/PbS Quantum Dot Heterojunction Photovoltaics Using a MoO₃ Interfacial Layer

Abstract

The ability to engineer interfacial energy offsets in photovoltaic devices is one of the keys to their optimization. Here, we demonstrate that improvements in power conversion efficiency may be attained for ZnO/PbS heterojunction quantum dot photovoltaics through the incorporation of a MoO(3) interlayer between the PbS colloidal quantum dot film and the top-contact anode. Through a combination of current-voltage characterization, circuit modeling, Mott-Schottky analysis, and external quantum efficiency measurements performed with bottom- and top-illumination, these enhancements are shown to stem from the elimination of a reverse-bias Schottky diode present at the PbS/anode interface. The incorporation of the high-work-function MoO(3) layer pins the Fermi level of the top contact, effectively decoupling the device performance from the work function of the anode and resulting in a high open-circuit voltage (0.59 ± 0.01 V) for a range of different anode materials. Corresponding increases in short-circuit current and fill factor enable 1.5-fold, 2.3-fold, and 4.5-fold enhancements in photovoltaic device efficiency for gold, silver, and ITO anodes, respectively, and result in a power conversion efficiency of 3.5 ± 0.4% for a device employing a gold anode.

Selective contacts drive charge extraction in quantum dot solids via asymmetry in carrier transfer kinetics

“…The successful operation of CQDs in an efficient solar cell is strongly dependent on the material-processing strategies used in film formation. When CQD are synthesized in solution, they are usually capped by organic molecules that employ long chains (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) carbons) to avoid agglomeration. Optimum photovoltaic operation of the CQD film requires the replacement of such ligands with short organic bidentate linkers, such as ethanedithiol or mercaptopropionic acid (MPA).…”

“…Interfacial engineering to obtain efficient electrical contacts is a central effort of the field 8 . It has been recognized that contacts determine device operation for CQD films used in applications of solar cells as well as photodetectors, which has led to the investigation of different materials such as MoO 3 hole-selective layers, organic and nanostructured contact materials [9][10][11][12][13] .…”

An Enhanced UV–Vis–NIR an d Flexible Photodetector Based on Electrospun ZnO Nanowire Array/PbS Quantum Dots Film Heterostructure

“…Recently, PbS QDs have attracted attention for NIR detection applications because of their inherent narrow (1.3 eV)23 and tunable bandgap altered with size and composition 24, 25, 26. The broadening of sensitive spectral range of ZnO NWs by combination with PbS QDs has been demonstrated in solar cells 27.…”

Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime

“…They enable bandgap tuning via adjustment of the nanoparticle size 1,2 . This has led to promising optoelectronic devices for lighting 3,4 , solar power conversion [5][6][7][8][9] and photon detection 10,11 . In solar cells, these materials have recently exceeded 7% certified power conversion efficiency (PCE) 5,12,13 , offering a promising path towards efficient, low-cost and roll-to-roll processed photovoltaics (PVs).…”