We analyze the adoption of clean technology by heterogeneous firms subject to financing constraints. In the model, capital goods differ in terms of their energy needs and age. In equilibrium, cleaner and newer capital requires more financial resources. Therefore, financial constraints induce an endogenous pattern in clean technology adoption: Financially constrained, smaller firms optimally invest in dirtier and older capital than unconstrained, larger firms. The model is consistent with the empirical patterns of technology adoption we document using data on commercial shipping fleets. We use a calibrated version of our model to simulate the aggregate transition dynamics to cleaner technology.