and renewable or earth abundant materials. [ 1,2 ] For photovoltaic panels, the energy recovery time is the length of operation of a panel required to generate the energy used to manufacture the panel. In thin fi lm inorganic panels, this time has dropped to about one year. [ 3 ] One of the revolutionary appeals of roll-to-roll manufacturing of organic photovoltaics (OPV) is the potential to achieve energy recovery times as low as 10 d. [ 4 ] Tremendous advances have recently been made in OPV effi ciencies, [ 5 ] all based on optimization of the bulk-heterojunction (BHJ) motif. [ 6,7 ] The performance of a BHJ requires the optimization of both its molecular-scale order and its nanometer-scale domain structure. [ 8 ] In general, the optimized structure is not at equilibrium. Many techniques have been employed for BHJ fi lm optimization, [ 9 ] including solvent choice and post deposition thermal [ 10 ] or vapor annealing. [ 11 ] Recently, formulations using low volatility liquid additives to achieve higher effi ciencies without thermal treatment have become popular. [12][13][14] Although additives such as 1,8-octanedithiol (ODT) and 1-chloronaphthalene (CN) have almost ubiquitous benefi cial effects, there is no consensus on either the origin or mechanism of their effi cacy. In some systems, additives cause smaller domains, [ 15,16 ] while in others they cause larger domains. [ 12,17 ] The effi cacy of ODT and diiodooctane has been attributed to selective solvation of the fullerene, enabling improved polymer order. CN, however, is typically a good solvent for both polymer and fullerene and thus must act via a different mechanism.We recently employed real-time optical techniques to study the mechanism by which the additives ODT and CN infl uence the solidifi cation of the poly(3-hexylthiophene):phenyl-C61butyric-acid-methyl-ester (P3HT:PCBM) BHJ. [ 18 ] Both additives promoted a greater than 5× improvement in device effi ciency over the additive-free fi lm in the absence of thermal annealing. Post-deposition characterization with ultraviolet-visible absorption spectroscopy (UV-Vis) and grazing incidence X-ray diffraction (GIXD) established that the additives increased the polymer's local order and crystallinity. Additionally, energy-fi ltered transmission electron microscopy (EF-TEM) revealed that the The most successful active fi lm morphology in organic photovoltaics is the bulk heterojunction (BHJ). The performance of a BHJ arises from a complex interplay of the spatial organization of the segregated donor and acceptor phases and the local order/quality of the respective phases. These critical morphological features develop dynamically during fi lm formation, and it has become common practice to control them by the introduction of processing additives. Here, in situ grazing incidence X-ray diffraction (GIXD) and grazing incidence small angle X-ray scattering (GISAXS) studies of the development of order in BHJ fi lms formed from the donor polymer poly(3-hexylthiophene) and acceptor phenyl-C61-butyric acid methyl e...

Optimized spin-coating and blade-coating are found to produce similar performance yet notably different morphologies.