2, ZAE, Bayern, Erlangen, , Germany
3, FAU Erlangen, Erlangen, , Germany
In this presentation, we introduce innovative approaches for the stabilization of ideally packaged (encapsulated) and completely unpackaged organic solar cells. While ideally packaged devices allow to study the intrinsic stability limitations of the device, solar cells fully exposed to the environment allow to investigate methods for preventing photo-oxidation of photoactive materials, thus alleviating the need for costly barrier materials.
We first compare the lifetime of continuously light soaked, ideally packaged polymer:fullerene (P3HT:PC60BM) and polymer:non-fullerene (P3HT:IDTBR) solar cells in the course of 2000 h to conclude that replacing PCBM with IDTBR fully inhibits short-circuit current losses. In fact, even the open circuit voltage and fill factor are only minimally affected, leading to photovoltaic devices with no burn-in (early, exponential loss in device performance), as opposed to P3HT:PCBM that shows a very pronounced burn-in. We elucidate the device physics of pristine and degraded devices for both material systems and identify clear differences in charge trapping and carrier lifetime behavior. Importantly, the stabilization extends to polymers with very different molecular weights.
We then present a pronounced photo-stabilization effect in air in a wide range of prominent semiconducting polymers in the presence of the antioxidant nickel(II) dibutyldithiocarbamate, Ni(dtc)2. We show that Ni(dtc)2 acts as a broadband stabilizer that inhibits both the formation of reactive radicals and singlet oxygen. Ultrafast pump–probe spectroscopy reveals quenching of triplet excited states as the central mechanism of singlet-oxygen induced photo-oxidation. When introduced into the active layer of organic photovoltaic devices, Ni(dtc)2 retards the short circuit current loss in air without affecting the sensitive morphology of bulk heterojunctions and without major sacrifices in semiconductor properties. We conclude that antioxidants based on nickel complexes render organic semiconductors less susceptible to oxygen and represent a cost-effective route toward organic electronic appliances with extended longevity.
 Nicola Gasparini, Michael Salvador, Sebastian Strohm, Thomas Heumueller, Ievgen Levchuk, Andrew Wadsworth, James H Bannock, John C de Mello, Hans-Joachim Egelhaaf, Derya Baran, Iain McCulloch, Christoph J Brabec, Adv. Energy Mater., 7, 1700770 (2017).
 Michael Salvador, Nicola Gasparini, José Darío Perea, Sri Harish Paleti, Andreas Distler, Liana N Inasaridze, Pavel Troshin, Larry Lüer, Hans-Joachim Egelhaaf, Christoph J Brabec, Energy Environ. Sci., 10, 2005-2016 (2017).