Density functional theory (DFT) is an ideal method for a large range of systems due to its balance between accuracy and computational efficiency. However, one of the key factors influencing its performance in practice is the choice of basis set, where minimal, localized basis sets often compete with extended, systematic basis sets. Wavelets, however, offer both locality and systematicity, as well as built-in multiresolution capabilities. Wavelet-based DFT therefore allows for the possibility of very precise simulations, while also being particularly suited to large, inhomogenous systems. In this talk I will discuss two different use-cases for wavelet-based DFT: the calculation of core spectra using the high precision all-electron approach employed in the MADNESS code, and the ability to treat thousands of atoms using the linear-scaling approach in the BigDFT code. I will focus on the application to organic LEDs (OLEDs), where these approaches may be used to give complementary insights into the electronic structure of OLED emitters. Furthermore, by treating large systems it also becomes possible to take into account the influence of disorder and environmental effects, which can both have an important impact on OLED properties.