Access to finance is a major barrier to clean innovation. We incorporate heterogeneous and endogenous financing costs in a directed technical change model and identify optimal climate mitigation policies. The presence of a financing experience effect induces more ambitious policies in the short-term, both to shift innovation and production towards clean sectors and to reduce the financing cost differential across technologies, which further facilitates the transition. The optimal climate policy mix between carbon taxes and clean research subsidies depends on whether experience is gained through clean production or research. In our benchmark scenario, where clean financing costs decline as cumulative clean output increases, we find an optimal carbon price premium of 47% in 2025, relative to a case with no financing costs.