Research in thermally-activated delayed fluorescence (TADF) emitters is gathering momentum and rapidly progressing towards commercial application in display industry. Successful TADF combines design strategies that result in thermal up-conversion of nonemissive triplets into emissive singlet excitons, increasing the maximum internal efficiency from 25 to 100 % in purely organic systems. Its performance can therefore compete with current leading emitters used in industry, however it is not without its hurdles and a full understanding of how to produce efficient TADF systems and stable organic light-emitting diodes (OLEDs) is still elusive. This thesis aims at illuminating strategies to achieve highly efficient and stable TADF. By examining the photophysical aspects of different donor-acceptor systems (D-A, D2-A, D3- A, D4-A and D-A-D) and, more importantly, establishing comparisons between different subsets of molecules, subtle but important aspects of the performance of these emitters are isolated to allow understanding of future design rules for better combinations. These comparisons are then correlated with the emitters' performance in devices. In a multi-donor platform, the inherent TADF mechanism and in host are both considered by comparing the effect of number and position of donors as well as rigidity and polarity of the host environment to the D-A angles. A separate comparative study elucidates the real heavy atom effect in an emitter with dual emission from two different conformations. Furthermore, the application of a well-established spectroscopy technique novel to TADF tests its physical mechanism by probing character and mixing of the excited states involved. Finally, in a more application-driven approach, a combination of three different TADF molecules for the production of white light is studied in simple device structures. In this sense, guidelines of how to produce optimised TADF systems emerge, moving the technology ever close to its industrial application.