Suppressing Interfacial Dipoles to Minimize Open‐Circuit Voltage Loss in Quantum Dot Photovoltaics

Abstract

Quantum‐dot (QD) photovoltaics (PVs) offer promise as energy‐conversion devices; however, their open‐circuit‐voltage (VOC) deficit is excessively large. Previous work has identified factors related to the QD active layer that contribute to VOC loss, including sub‐bandgap trap states and polydispersity in QD films. This work focuses instead on layer interfaces, and reveals a critical source of VOC loss: electron leakage at the QD/hole‐transport layer (HTL) interface. Although large‐bandgap organic materials in HTL are potentially suited to minimizing leakage current, dipoles that form at an organic/metal interface impede control over optimal band alignments. To overcome the challenge, a bilayer HTL configuration, which consists of semiconducting alpha‐sexithiophene (α‐6T) and metallic poly(3,4‐ethylenedioxythiphene) polystyrene sulfonate (PEDOT:PSS), is introduced. The introduction of the PEDOT:PSS layer between α‐6T and Au electrode suppresses the formation of undesired interfacial dipoles and a Schottky barrier for holes, and the bilayer HTL provides a high electron barrier of 1.35 eV. Using bilayer HTLs enhances the VOC by 74 mV without compromising the JSC compared to conventional MoO3 control devices, leading to a best power conversion efficiency of 9.2% (>40% improvement relative to relevant controls). Wider applicability of the bilayer strategy is demonstrated by a similar structure based on shallow lowest‐unoccupied‐molecular‐orbital (LUMO) levels.

Stability of Quantum Dot Solar Cells: A Matter of (Life)Time

“…[80,81] While this approach showed promising results, the stability of the transport layers needs to be improved further. [82][83][84][85][86][87][88] Another interesting passivation route involves the introduction of a layer of carbon nanotubes between the EDT layer and the gold anode, as reported by Salazar-Rios et al [74] in 2018. It was found that a single-walled carbon nanotube (SWCNT) layer significantly improved cell stability under illumination, which maintained 85% of its initial PCE after 105 h of continuous In the pristine state (before oxygen exposure) surface traps are present, so charge recombination between dots is uninhibited and leakage pathways remain open.…”

Highly Stable Interdigitated PbS Quantum Dot and ZnO Nanowire Solar Cells with an Automatically Embedded Electron-Blocking Layer

“…Interface recombination and low stability remain the major bottlenecks of electron-blocking and hole-transport layers. 33,34 Previously, we fabricated approximately 1 μm-long ZnO nanowires (NWs) and constructed heterojunction CQD solar cells without any particular EBLs; the solar cell was composed of a PbS QD−ZnO NW interdigitated layer sandwiched between a transparent conductive oxide layer and a Au electrode 37,38 (Figure 1b). The longer NWs produce higher EQE in the infrared region.…”

Surface restoration of polycrystalline Sb2Se3 thin films by conjugated molecules enabling high-performance photocathodes for photoelectrochemical water splitting

“…It was also reported that the insertion of a molecular dipole layer at the interface of the p-and n-type materials can shift the relative band position to enhance the Vph [15,16]. Wick-Joliat et al recently elucidated that the insertion of phosphonic acid dipole layer at Si/TiO2 can significantly improve the onset potential of Si photocathode up to 400 mV as supported by both theoretical calculation and experimental observation [17].…”