This thesis focuses on the outdoor monitoring of organic photovoltaics (OPVs) with the aim of improving the stability and performance of OPVs under real world conditions. This is important as in order for OPVs to become commercially viable they must make the transition from small laboratory cells to larger modules. Over the course of several outdoor monitoring campaigns various types of OPV modules have been benchmarked against a number of other technologies: polycrystalline silicon, cadmium indium diselenide and dye sensitised solar cells. The principal performance parameters are examined in detail, analysing their dependence on irradiance and temperature. OPVs were shown to have positive temperature coefficients for efficiency, ISC and fill factor and a negative temperature coefficient for VOC. One of the main causes of degradation is ingress of water and oxygen into the module and subsequent photo-oxidation of the active layer and it was shown that UV filtering would improve stability. To improve the yield of OPVs outdoors, modules were laminated to different corrugated substrates and subjected to indoor characterisation and outdoor monitoring. The corrugated modules were shown to have three advantages: the effective area of the module, allowing for curvature, is reduced which leads to an improvement in the power conversion efficiency per unit area; substantial enhancement at high angles of incidence led to increased output during early morning and evening; under diffuse irradiance performance improved by up to 25%. Outdoor measurements on larger module strips showed that corrugated strips outperformed flat strips by 7.5% with a 14.8% enhancement under diffuse conditions. An alternative technique to improve the yield of OPVs is the use of luminescent down-shifting coatings which were investigated as alternatives to UV filters and have the added benefit of improving stability. The use of both discrete and multiple-dye blends dispersed in poly(methyl methacrylate) led to improvements in performance of up to 8% and a six-fold extension of operational lifetime. Dyes were systematically selected by examining their absorption and photoluminescence spectra and matching these to the spectral performance of P3HT:PC61BM OPV devices. In doing so optimised multiple-dye blends were made possible.