Effect of Processing Additives on the Solidification of Blade‐Coated Polymer/Fullerene Blend Films via In‐Situ Structure Measurements

Abstract

The use of processing additives has emerged as a powerful approach for the optimization of active layer performance in organic photovoltaic devices. However, definitive physical mechanisms explaining the impact of additives have not yet been determined. To elucidate the role of additives, we have studied the time evolution of structure in polymer‐fullerene films blade‐coated from additive containing solutions using in‐situ spectroscopic ellipsometry and UV–vis transmission. Additives that are poor solvents for poly(3‐hexylthiophene) (P3HT), such as 1,8‐octanedithiol, and additives that are good solvents for P3HT, such as 1‐chloronapthalene, both promote improved polymer order, phase segregation, and device performance. Regardless of the presence or type of additive, the polymer order develops under conditions of extreme supersaturation. Additives, regardless of whether they are solvents for P3HT, promote earlier polymer aggregation compared to additive ‐ free solutions presumably by degrading the solvent quality. We find evidence that the details of the final film morphology may be linked to the influence of the substrate and long‐time film plasticization in the cases of the non‐solvent and solvent respectively.

Controlling additive behavior to reveal an alternative morphology formation mechanism in polymer : fullerene bulk-heterojunctions

“…polymer ordering. [32][33][34][35][36][37] Although these studies provided invaluable information on the matter, there are very few examples of additives with different solubility behaviors; hence the current understanding on the relationship between solution thermodynamics and drying kinetics of such thin lms is not detailed enough to build a roadmap for producing better ink formulations for the purpose of upscaling.…”

Real-time evaluation of thin film drying kinetics using an advanced, multi-probe optical setup

“…Thus, in the last few years in situ measurements from blading and bar spreading methods became as popular as spin coating due to their similarities to industrial-scale printing methods. 7,8,[11][12][13][14][15]20,21,23,25 Nevertheless, regardless of whether spin coating is selected or doctor blading, in situ characterization methods are mostly utilized to get deeper insight into the morphology and correlate this information with device performance. There is a very limited amount of reports which studied the precision of solution formulation and drying conditions on the thermodynamics and kinetics of the BHJ thin film drying, thus the current knowledge is still far from building a road map for better solution formulations and drying conditions, which could be transferred to large-scale processing for further optimizations.…”

A real-time study of the benefits of co-solvents in polymer solar cell processing

“…The dynamics of solvent evaporation and phase separation govern the final structure. In situ studies have been performed on timescales corresponding to realistic processing conditions for practical applications [31][32][33][34] . However, in none of these systems co-solvents are necessary to decrease domain sizes.…”