The alcohol and water-based processing of a perylene diimide (PDI) organic semiconductor into large area and solvent resistant films is reported. The compound, PDIN-H, is an N-annulated PDI dye with...

We investigate the effect of adding an N-annulated perylene diimide dye with a pyrrolic NH functional group (PDIN-H) onto an electron extraction layer (EEL) in a bilayer configuration (ZnO/PDIN-H) on the photostability of inverted organic solar cells (OSCs). To do so, we insert a thin layer of PDIN-H in between the ZnO layer and the bulk heterojunction (BHJ) active layer. Results show that under prolonged ultraviolet (UV) irradiation, the cells with the ZnO/PDIN-H EEL exhibit substantially higher photostability compared to the reference cells with only ZnO, leading to respective T 80 values of ≳780 h versus only ∼124 h, where T 80 is the time before the power conversion efficiency (PCE) decreases to 80% of its initial value. The higher PCE photostability arises primarily from the more stable open-circuit voltage (V oc) and fill factor (FF) under UV stress. Changes in the dark reverse current characteristics of the cells show that the higher V oc stability acquired upon adding PDIN-H on top of ZnO is mainly due to the ability of the ITO/ZnO/PDIN-H contact to maintain the blockage of hole injection even after UV stress. Analysis of the voltage dependence of dark and light ideality factors verifies that inserting PDIN-H prevents to a significant extent the UV-induced surface recombination that is observed at the ZnO/active-layer interface, thus enhancing the cells’ photostability. Results from hole-only devices and ultraviolet photoelectron spectroscopy reveal that the passivation of ZnO surface defects by PDIN-H is the primary origin of suppressing the UV-induced surface recombination and thereby increasing the photostability. The findings provide not only critical insights into the substantial role of the electron collection contact in the photodegradation of OSCs but also strategies to control them that can be utilized well beyond the specific material system being studied here.

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Electroluminescence (EL) degradation mechanisms in solution-coated (SOL) host:guest (H:G) systems commonly used in phosphorescent organic light-emitting diodes (OLEDs) are investigated and compared to their vacuum-deposited (VAC) counterparts. Changes in the EL, photoluminescence (PL), and time-resolved PL (TRPL) characteristics of devices comprising SOL or VAC H:G light-emitting layers (EMLs) made of the same materials and in the same device architectures during prolonged electrical driving are compared and analyzed. Hole-only devices are also utilized to study the effects of charges and excitons, separately and combined. Moreover, devices with double EMLs comprising SOL and VAC components are tested to glean additional insights into the role of host excitons in device degradation. The results indicate that the faster degradation of SOL EML devices relative to their VAC EML counterparts under electrical stress is due–at least in part–to the less efficient host-to-guest (H → G) energy transfer in these systems, which accelerates molecular aggregation in the EML. Interactions between excitons and polarons in the EMLs induce this aggregation phenomenon which occurs more strongly in the case of SOL EMLs compared to their VAC counterparts because of the higher host exciton concentration in the former as a result of the less efficient H → G energy transfer. The findings shed light on one of the root causes of the limited stability of SOL OLEDs.