Organic and hybrid thin film electronic devices, such as memory diodes, solar cells and transistors, typically contain a functional layer based on a blend of multiple polymeric or small-molecular species whose properties cooperatively give rise to a specific function. Depending on the desired functionality, phase separation during thin film solution processing is either encouraged or suppressed. Usually, at least one blend component is polymeric, so that mutual repulsion readily overcomes the entropic driving force to form stable mixtures. For this reason, it is often observed that during solution-casting droplet-like demixed morphologies emerge due to (spontaneous) liquid-liquid (L-L) demixing. This presentation focuses on the role of this mode of phase separation in thin film electronics and how it is induced by mass exchange across the liquid-vapor boundary, i.e. solvent evaporation and vapor condensation. I give an overview on the work we have done to theoretically understand the influence of liquid-vapor exchange rates on demixing kinetics, as well as domain structure and composition. Multi-component continuum limit modeling demonstrates how microstructure and feature sizes emerge upon solvent evaporation and/or vapor condensation. The numerical simulations yield morphologies consistent with experimentally observed structures and demonstrate how domain size and phase composition are affected by internal and environmental factors.