Biomimetic approach to inhibition of photooxidation in organic solar cells using beta-carotene as an additive.

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 beta-carotene (BC), an inexpensive and green, naturally-occurring antioxidant, dramatically improves OPV stability. When compared to non-stabilized reference devices, the accumulated power generation in presence of BC of PTB7:[70]PCBM devices 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.