Large scale introduction of Perovskite based tandem solar cells is seen as promising high-efficiency, low-cost contributions to climate change mitigation. However, sustainability of perovskite cells has been questioned due to application of lead in the perovskite layer which may result in the release of lead to the environment and the human population. In this study, substance flow analysis was used to quantify potential lead emissions from production, use and end of life of perovskite in tandem solar cells. Lead emissions were translated into human toxicity and ecotoxicity impacts using life cycle assessment. Climate change impacts from electricity for perovskite production were also taken into account. These impacts are compared to the ones of the grid electricity that would otherwise have been used. Climate change and toxicity benefits and burdens are weighted using shadow prices. Our results show that environmental benefits from avoided grid electricity exceed environmental burdens from using perovskite based cells for climate change as well as for toxicity. We conclude that perovskite based cells can contribute to transition to renewable energy sources. Further research into lead encapsulation measures and worker exposure are recommended. (C) 2017 Elsevier Ltd. All rights reserved.