Transforming the energy infrastructure towards low-carbon technologies in both industrialized and developing countries is a critical part of the global greenhouse gas mitigation efforts that are necessary to limit dangerous climate change. Renewable Energy Feed-in tariffs (REFIT) have been crucial policy instruments to rapidly expand renewable electricity generation in Europe, and have been taken up in a rapidly increasing number of countries outside Europe in the last years. This policy paper argues that the Green Climate Fund (GCF) should become a key UNFCCC vehicle to support further diffusion of REFITs in developing countries to a level that mobilizes the hundreds of gigawatts of renewable energies required for a 2° C stabilization scenario. The GCF aims at making a “significant and ambitious contribution” to these efforts, guided by the principles of the UNFCCC. As the GCF is currently still emerging, we offer institutional design options that would allow facilitating rapid implementation, provided there is a sufficient capitalization.