Tuning Areal Density and Surface Passivation of ZnO Nanowire Array Enable Efficient PbS QDs Solar Cells with Enhanced Current Density

Abstract

Colloidal PbS quantum dots (QDs) have provoked a revolution in the field of optoelectronic devices owing to their low-cost fabrication processing and excellent physical properties. Recently, the fabrication of nanostructured PbS QDs photovoltaic (PV) devices based on zinc oxide (ZnO) nanowires array appeared as an effective strategy for improving the overall device performance. On This article is protected by copyright. All rights reserved. 2 the other hand, the infiltration of PbS QDs in a densely packed ZnO nanowire array not only impedes the efficient charge extraction but also increases the surface trap states and charge carrier recombination leading to degraded PV performance. Despite its potentially strong impact on the device performance, the role of nanowire areal density on photon absorption and exciton dynamicshas not yet been studied and still remains unexplored. Here, for the first time, we tune the areal density of ZnO nanowires through controlling the precursor concentration and study its impact on PbS QDs PV performance. It is found that the device with optimized ZnO nanowire areal density yields significantly increased power conversion efficiency (PCE) (10.1% vs. 8.5% of control nanowirebased device) due to improved light scattering and reduced surface recombination states. To further improve the photovoltaic performance, we treated the ZnO nanowire surface with hydrogen plasma, which has not been studied before in QDs PVs. Transient photovoltage (TPV) measurement reveal that this passivation process noticeably reduces the nonradiative charge recombination yielding a champion device with a remarkable PCE of 10.8%.

Inducing upwards band bending by surface stripping ZnO nanowires with argon bombardment

“…While a study published by Richters et al observed similar effects by in casing ZnO nanowires in Al 2 O 3 [6]. Recent work by Dastjerdi et al used hydrogen plasma to passivate surface states of ZnO nanowires and caused a reduction in defects observed with photoluminescence (PL) [7]. Other work carried out by Allen et al has shown that reactive oxygen species at the surface can influence the electrical properties and contact type [8,9].…”

A Review on the Effects of ZnO Nanowire Morphology on the Performance of Interpenetrating Bulk Heterojunction Quantum Dot Solar Cells

“…For effective light management in the IBHJ structures, too large or too small an area density leads to higher light reflectance, as shown in Figure 5 a, and an appropriate area density eventually leads to higher light absorption and higher J SC . Recently, Tavakoli Dastjerdi et al [ 93 ] obtained a champion device with a PCE of 10.1% by tuning the areal density of ZnO NWs (≈150 per μm 2 ) by controlling the precursor concentration. In short, the density control of NWs requires a balance between the interface area and the light trapping effect of NWs.…”

“…More recently, Tavakoli Dastjerdi et al [ 93 ] passivated ZnO NW surface states using the hydrogen plasma treatment. Compared with the untreated NWs, the PL spectrum of the H-plasma-treated ZnO NWs showed a clear enhancement of near-band emissions and a remarkable quenching of the visible emission peak.…”

Double‐Layer electron transporting layer for efficient lead sulfide quantum dots solar cells

“…Finding a suitable ETL in terms of mobility, band alignment and stability can improve the efficiency and stability of the device [27]. In PbS QDs PVs, ZnO is the commonly used materials for ETL, which normally shows a good PCE [22]. However, the loss‐in‐potential in PbS QDs PV is still remained a big challenge.…”

“…Recently, extensive efforts have been devoted to this PV technology in order to further improve the device performance, resulting in a certified power conversion efficiency (PCE) of 12% [8][9][10][11][12]. There are couple of strategies for this purpose such as new ligand passivation approaches [13], architectural engineering [14][15][16], interface engineering [17][18][19][20], employment of nanostructured substrates [21,22], plasma and ultraviolet (UV) light treatments [13,22], employment of down-shifting materials [23][24][25] etc. Basically, in a QDs solar cell, the interface of PbS QDs layer/ electron transporting layer (ETL) plays a critical role in the device performance [26].…”