Biomimetic Approach to Inhibition of Photooxidation in Organic Solar Cells Using Beta-Carotene as an Additive

Abstract

Recent efficiency records of organic photovoltaics (OPV) highlight stability as a limiting weakness. Incorporation of stabilizers is a desirable approach for inhibiting degradationit is inexpensive and readily up-scalable. However, to date, such additives have had limited success. We show that β-carotene (BC), an inexpensive and green, naturally occurring antioxidant, dramatically improves OPV stability. When compared to nonstabilized reference devices, the accumulated power generation of PTB7:[70]­PCBM devices in the presence of BC increases by an impressive factor of 6, due to stabilization of both the burn-in and the lifetime, and by a factor of 21 for P3HT:[60]­PCBM devices, owing to a longer lifetime. Using electron spin resonance and time-resolved near-IR emission spectroscopies, we probed radical and singlet oxygen concentrations. We demonstrate that singlet oxygen sensitized by [70]­PCBM causes the “burn-in” of PTB7:[70]­PCBM devices and that BC effectively mitigates it. Our results provide an effective solution to the problem that currently limits widespread use of OPV.

Structure dependent photostability of ITIC and ITIC-4F

“…44 We claim that under the specific experimental conditions of light and oxygen exposure employed in this study, the radical cation chain reaction can easily initiate, as the high HOMO level of alkenes can facilitate the electron transfer from alkenes to oxygen. Other mechanisms involving the presence of photosensitized production of singlet oxygen may also contribute to degradation of organic photovoltaic materials, as recently reported by Turkovic et al 45 On the other side, fluorine substitution in the end-group of the ITIC molecule increases the non-covalent interactions with the consequent introduction of a favored cell packing. 46 Moreover, fluorination lowers the HOMO/LUMO levels, increases the electron affinity 47 and enhances the molecular electron-pulling effect, with the result of a more efficient delocalization of the electron cloud over the electron-withdrawing site, and a reduced oxidative effect.…”

Degradation Behavior of Scalable Nonfullerene Organic Solar Cells Assessed by Outdoor and Indoor ISOS Stability Protocols

“…The irreversible efficiency loss is driven by short-circuit current density ( J SC ) and fill factor (FF) loss (Figure 3b,d), which could be a consequence of photoinduced fullerene dimerization, as previously reported by Heumueller et al [17] Also, singlet oxygen-based degradation has recently been pointed on for specific PC 60/70 BM-based systems. [8][9][10] The most notable result of the outdoor testing is the presence of reversible degradation, i.e., degradation occurs when the device is illuminated, but after storing the device in the dark, the efficiency recovers. This effect appears to be primarily driven by V OC and (to a lesser extent) J SC (Figure 3b,c).…”

“…Extrinsic mechanisms, such as oxygen, water, UV exposure, and mechanical stress, can be largely controlled through the engineering of encapsulation barriers and use of device additives. [8][9][10][11][12] Intrinsic mechanisms include the effects of heat and light on the device structure and electronic properties, [13][14][15] which can only be mitigated by altering the materials or structure of the device itself. In addition, the device processing, or purity of material, may also introduce oxygen or other defects into the device structure prior to encapsulation.…”

“…[16][17][18] In specific systems it also includes singlet oxygen initiated degradation processes as recently demonstrated. [10,19,20] However, NFAs are not without their own stability issues. While some NFA-based devices have been shown to exhibit excellent thermal stability, [21] they are often fabricated using processing additives that can be detrimental to device lifetime.…”

Synthesis and properties of quinazoline-based versatile exciplex-forming compounds

“…Photoelectron emission spectroscopy measurement was performed according to the procedure reported in literature [27]. OLED fabrication and characterization was carried out according to the procedure reported earlier [28].…”