The nature of one and two-photon absorption enhancement in a series of oligothiophene dendrimers, recently proposed for applications in entangled photon sensors and solar cells, has been analyzed using both theory (time dependent density functional theory calculations) and experiment (fluorescence upconversion measurements). The linear absorption spectra exhibit a red shift of the absorption maxima and broadening as a function of dendrimer generations. The two-photon absorption cross sections increase sharply with the number of thiophene units in the dendrimer. The cooperative enhancement in absorption two-photon cross sections is explained by (i) an increase in the excited-state density for larger molecules and (ii) delocalization of the low-lying excited states over extended thiophene chains. Fluorescence anisotropy measurements and examination of the calculated excited-state properties reveal that this delocalization is accompanied by a size-dependent decrease in excited-state symmetries. A substantial red shift of the emission maxima for larger dendrimers is explained through the vibronic planarization of the longest linear α-thiophene chain for the emitting excited state. For higher generations, the fluorescence quantum yield decreases due to increased nonradiative decay efficiency (e.g., intersystem crossing). The detailed information about the dendrimer 3D structure and excitations provides guidance for further optimizations of dendritic structures for nonlinear optical and opto-electronic applications.

The n‐i‐p type perovskite solar cells suffer unpredictable catastrophic failure under operation, which is a barrier for their commercialization. The fluorescence enhancement at Ag electrode edge and performance recovery after cutting the Ag electrode edge off prove that the shunting position is mainly located at the edge of device. Surface morphology and elemental analyses prove the corrosion of the Ag electrode and the diffusion of Ag+ ions on the edge for aged cells. Moreover, much condensed and larger Ag clusters are formed on the MoO3 layer. Such a contrast is also observed while comparing the central and the edge of the Ag/Spiro‐OMeTAD film. Hence, the catastrophic failure mechanism can be concluded as photon‐induced decomposition of the perovskite film and release reactive iodide species, which diffuse and react with the loose Ag clusters on the edge of the cell. The corrosion of the Ag electrode and the migration of Ag+ ions into Spiro‐OMeTAD and perovskite films lead to the forming of conducting filament that shunts the cell. The more condensed Ag cluster on the MoO3 surface as well as the blocking of holes within the Spiro‐OMeTAD/MoO3 interface successfully prevent the oxidation of Ag electrode and suppress the catastrophic failure.

Roll-to-roll (R2R) micro-gravure printing is an attractive technology for fabricating organic solar cells (OSCs) at low cost with high throughput. The nanoscale morphology and phase separation of R2R micro-gravure printed active layers have a large influence on the photovoltaic performance of OSCs. Herein, we demonstrate that the photovoltaic performance of R2R micro-gravure printed P3HT: PCBM OSCs can be enhanced by optimizing phase separation using solvent engineering. R2R microgravure printed P3HT:PCBM blend film with chlorobenzene solvent enabled optimized phase separation and formation of a fine-tuned interpenetrating network in a bulk heterojunction (BHJ) layer compared with a film with 1,2-dicholorobenzene solvent. This creates an optimal transport pathway and therefore effectively enhances charge transport in the BHJ blend film and boosts device performance. This research shows that high-performance OSCs could be fabricated by large-scale, R2R micro-gravure printing with solvent engineering, which would accelerate the development of fully R2R micro-gravure printed flexible OSCs.