Improving Thermal and Photostability of Polymer Solar Cells by Robust Interface Engineering

Abstract

As the power conversion efficiency (PCE) of organic photovoltaics (OPVs) approaches 19%, increasing research attention is being paid to enhancing the device's long‐term stability. In this study, a robust interface engineering of graphene oxide nanosheets (GNS) is expounded on improving the thermal and photostability of non‐fullerene bulk‐heterojunction (NFA BHJ) OPVs to a practical level. Three distinct GNSs (GNS, N‐doped GNS (N‐GNS), and N,S‐doped GNS (NS‐GNS)) synthesized through a pyrolysis method are applied as the ZnO modifier in inverted OPVs. The results reveal that the GNS modification introduces passivation and dipole effects to enable better energy‐level alignment and to facilitate charge transfer across the ZnO/BHJ interface. Besides, it optimizes the BHJ morphology of the photoactive layer, and the N,S doping of GNS further enhances the interaction with the photoactive components to enable a more idea BHJ morphology. Consequently, the NS‐GNS device delivers enhanced performance from 14.5% (control device) to 16.5%. Moreover, the thermally/chemically stable GNS is shown to stabilize the morphology of the ZnO electron transport layer (ETL) and to endow the BHJ morphology of the photoactive layer grown atop with a more stable thermodynamic property. This largely reduces the microstructure changes and the associated charge recombination in the BHJ layer under constant thermal/light stresses. Finally, the NS‐GNS device is demonstrated to exhibit an impressive T80 lifetime (time at which PCE of the device decays to 80% of the initial PCE) of 2712 h under a constant thermal condition at 65 °C in a glovebox and an outstanding photostability with a T80 lifetime of 2000 h under constant AM1.5G 1‐sun illumination in an N2‐controlled environment.

High-Efficiency Semitransparent Organic Photovoltaics Containing Vertical Multiheterojunctions

“…Among our various films, the visible region transmittance of the SD trilayer devices increased the most upon decreasing the polymer donor/small-molecule acceptor thickness ratio, yet their NIR transmittances remained almost constant . Relative to the PL intensity of the neat polymer D18, those of the BHJ and SD bilayer films decreased by 79.2 and 95.6%, respectively (Figure c); notably, the SD trilayer film exhibited the largest PL intensity quenching of 98.8%, indicating that it featured the most efficient charge separation. , Figure d provides plots of the corrected photocurrent ( J ph / J sat ) with respect to the effective voltage ( V eff = V 0 – V ), where J sat represents the saturation current density, V 0 the voltage when J ph equals to 0, and V the applied voltage. , At low values of V eff (ca. 0.01–0.5 V), the SD trilayer device had the highest values of J ph / J sat , consistent with the PL quenching behavior of its active layer.…”

“…36,37 Figure 2d provides plots of the corrected photocurrent (J ph /J sat ) with respect to the effective voltage (V eff = V 0 − V), where J sat represents the saturation current density, V 0 the voltage when J ph equals to 0, and V the applied voltage. 38,39 At low values of V eff (ca. 0.01−0.5 V), the SD trilayer device had the highest values of J ph /J sat , consistent with the PL quenching behavior of its active layer.…”

Vitamin C for Photo-Stable Non-fullerene-acceptor-Based Organic Solar Cells

“…In addition, its low cost, easy synthesis, and simple solution processability makes it industrially viable. , Despite these advantages, ZnO ETL is photocatalytically active, which leads to decomposition and photooxidation of organic molecules (e.g., NFA) on the surface of ZnO, via redox reactions and formation of hydroxyl radicals . This, subsequently, leads to charge accumulation and recombination at the ZnO interface, which both strongly reduce the device stability. ,, Various approaches have been explored to control such interfacial degradation: Su and co-workers utilized nitrogen and sulfur-doped graphene oxide nanosheets (NS-GNSs) as a modifier layer for ZnO; Hu et al used aqueous polyethylenimine as a modifier layer; Liu et al developed modified ZnO layers, Me–ZnO, DMSO-ZnO, and sol–gel-ZnO; and Xu et al used C60 self-assembled monolayer (SAM) as a protective buffer layer . Recently, Aryal et al demonstrated that 2D Mxene could be embedded with ZnO to reduce this photocatalytic decomposition on ZnO surface .…”

“…31 This, subsequently, leads to charge accumulation and recombination at the ZnO interface, which both strongly reduce the device stability. 29,34,35 Various approaches have been explored to control such interfacial degradation: Su and co-workers 36 utilized nitrogen and sulfur-doped graphene oxide nanosheets (NS-GNSs) as a modifier layer for ZnO; Hu et al 37 used aqueous polyethylenimine as a modifier layer; Liu et al 38 developed modified ZnO layers, Me−ZnO, DMSO-ZnO, and sol−gel-ZnO; and Xu et al used C60 self-assembled monolayer (SAM) as a protective buffer layer. 39 Recently, Aryal et al demonstrated that 2D Mxene could be embedded with ZnO to reduce this photocatalytic decomposition on ZnO surface.…”

High-Performance Ternary Organic Photovoltaics Incorporating Small-Molecule Acceptors with an Unfused-Ring Core

“…OPVs appear likely to complement or replace traditional solar cells in applications such as power source for greenhouse lighting, indoor light harvesting, floating photovoltaics (PVs), and self-powered wearable sensors/smart clothing. − Very recently, great strides have been made in overcoming the low power conversion efficiencies (PCEs) and instabilities, further promoting this technology toward practical commercialization. Several publications have demonstrated single-junction OPVs displaying breakthrough PCEs (> 18%) − and superior long-term stability when exposed to light, heat, or air (without encapsulation). ,− These advances in the performance characteristics of OPVs can be attributed to the successful development of non-fullerene acceptors (NFAs), which possess highly tunable chemical structures ranging from small molecules to oligomers and polymers as well as outstanding optoelectronic properties. − …”