Abstract
Organic photovoltaics are a sustainable and cost-effective power-generation technology that may aid the move to zero-emission buildings, carbon neutral cities, and electric vehicles. While state-of-the-art organic photovoltaic devices can be encapsulated to withstand air and moisture, they are currently still susceptible to light-induced degradation, leading to a decline in the long-term efficiency of the devices. In this study, the role of ultraviolet (UV) radiation on a multilayer organic photovoltaic device is systematically uncovered using spectral filtering. By applying long-pass filters to remove different parts of the UV portion of the AM1.5G spectrum, two main photodegradation processes are shown to occur in the organic photovoltaic devices. A UV-activated process is found to cause a significant decrease in the photocurrent across the whole spectrum and is most likely linked to the deterioration of the charge extraction layers. In addition, a photodegradation process caused by UV-filtered sunlight is found to change the micromorphology of the bulk heterojunction material, leading to a reduction in photocurrent at high photon energies. These findings strongly suggest that the fabrication of inherently photostable organic photovoltaic devices will require the replacement of fullerene-based electron transporter materials with alternative organic semiconductors.
Highlights
Photovoltaic devices have made significant inroads into becoming one of the more prominent renewable energyharvesting technologies.[1]
PCBM absorbs, suggesting a link with changes in this component. To examine whether this reduction in external quantum efficiency (EQE) is caused by the oligomerization of PCBM, we carefully explore any additional changes that may occur below where CT state photocurrent features may tchoenbtrainbdutgea.5p2−E5g4, Because the CT state arises from an overlap between the frontier molecular orbitals of the acceptor and the donor, even a minute change in the morphology of the heterojunction, caused, e.g., by the oligomerization of PCBM, will affect the number of free charges generated from the CT state
As we have argued above, the observed photodegradation in the presence of UVB + UVA-filtered AM1.5 light is predominantly caused by changes in the PCBM component that affect the CT states formed at the PBTZT-statBDTT-8/PCBM heterojunction
Summary
Photovoltaic devices have made significant inroads into becoming one of the more prominent renewable energyharvesting technologies.[1]. Two main types of organic semiconductors are currently used in photovoltaic devices, which are small organic molecules such as fullerenes and polymer-based semiconductors such as poly(3-hexylthiophene-
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