Energy alignment and recombination in perovskite solar cells: weighted influence on the open circuit voltage

In this work, we assess the possible reasons for the differences observed in open circuit voltage (VOC) in mixed cation perovskite solar cells when comparing four different hole transport materials (HTMs), namely TAE‐1, TAE‐3, TAE‐4 and spiro‐OMeTAD. All these HTMs present close chemical and physical properties. Additionally to the evaluation of the HTM influence on recombination, we find that, upon deposition of the organic HTM on top of the perovskite, there is an important change in the energy levels position, and the impact on the device VOC is discussed. We consider that this experimental observation could be general for other organic HTMs and would justify the difficulties for finding molecules and materials that could improve the efficiency of perovskite solar cells overcoming the solar‐to‐energy conversion efficiency of solar cells made using spiro‐OMeTAD as holes selective contact.EP and AVF thank MINECO (projects CTQ2013-47183 and CTQ2017- 89814-P). NM thanks the European Research Council (ERC-320441- Chirallcarbon), the CAM (Y2018/NMT-4783QUIMTRONIC-CM) and the Spanish Ministry of Economy and Competitiveness MINECO (projects CTQ2014-52045-R, CTQ2015-71154-P, CTQ2016-80042-R, CTQ2017-83531-R and CTQ2016-81911-REDT). NM also thanks the Alexander von Humboldt Foundation and the Unidad de Excelencia Severo Ochoa SEV-2016-0686 is acknowledged. EP and AV are also grateful to ICIQ and ICREA for economical support. EB and CO thank the Generalitat de Catalunya 2017 SGR668 and 2017 SGR669, the MINEICO projects MAT2016-77852-C2-1-R (AEI/FEDER, UE), MAT2015-68994-REDC and the ‘‘Severo Ochoa’’ Program for Centers of Excellence in R&D (SEV-2015-0496). IG thanks Jesús Jiménez López for the fruitful discussions.Peer reviewe