Comment on “Tremendously enhanced photocurrent enabled by triplet–triplet annihilation up-conversion for high-performance perovskite solar cells” by W. Sheng, J. Yang, X. Li, G. Liu, Z. Lin, J. Long, S. Xiao, L. Tan and Y. Chen, Energy Environ. Sci., 2021, 14, 3532

Sheng et al. (2021) report an increase in the power conversion efficiency of a methylammonium lead iodide perovskite solar cell, which they have attributed to the benefits of in situ perovskite-sensitized upconversion by triplet–triplet annihilation in the organic semiconductor rubrene. In the following, we will discuss why in the device structure presented here upconversion inherently cannot be the underlying cause of the observed effects. Rather, the process of upconversion can fundamentally only lead to a reduction of the device efficiency if the same material is used as the active layer in the photovoltaic devices and as the triplet sensitizer. Therefore, the improved photovoltaic performance must have a different root cause. We follow up with an alternative interpretation for the performance increase observed by the authors.