Nanoscale Morphology of Doctor Bladed versus Spin-Coated Organic Photovoltaic Films

5 years ago

Nanoscale Morphology of Doctor Bladed versus Spin-Coated Organic Photovoltaic Films

Olga Wodo, Christoph J. Brabec, Joseph Sit, Adam J. Moule, Tayebeh Ameri, Derya Baran, Baskar Ganapathysubramanian, Balaji Sesha Sarath Pokuri

Recent advances in efficiency of organic photovoltaics are driven by judicious selection of processing conditions that result in a “desired” morphology. An important theme of morphology research is quantifying the effect of processing conditions on morphology and relating it to device efficiency. State-of-the-art morphology quantification methods provide film-averaged or 2D-projected features that only indirectly correlate with performance, making causal reasoning nontrivial. Accessing the 3D distribution of material, however, provides a means of directly mapping processing to performance. In this paper, two recently developed techniques are integrated—reconstruction of 3D morphology and subsequent conversion into intuitive morphology descriptors —to comprehensively image and quantify morphology. These techniques are applied on films generated by doctor blading and spin coating, additionally investigating the effect of thermal annealing. It is found that morphology of all samples exhibits very high connectivity to electrodes. Not surprisingly, thermal annealing consistently increases the average domain size in the samples, aiding exciton generation. Furthermore, annealing also improves the balance of interfaces, enhancing exciton dissociation. A comparison of morphology descriptors impacting each stage of photophysics (exciton generation, dissociation, and charge transport) reveals that spin-annealed sample exhibits superior morphology-based performance indicators. This suggests substantial room for improvement of blade-based methods (process optimization) for morphology tuning to enhance performance of large area devices. For optimizing the performance of organic photovoltaics, it is important to access the 3D distribution of material. This work integrates two recently developed techniques—reconstruction of 3D morphology and its conversion into intuitive morphology descriptors—to comprehensively image and quantify 3D morphology under spin-coating and doctor-blading processing conditions. The results suggest substantial room for improvement of blade-based methods.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/aenm.201701269