Despite the rapid increase in the efficiency (PCE) of perovskite solar cells, their open circuit voltage (V_oc) limits their commercialization. Contradictory results exist in the literature concerning the dependence of the V_oc on the ionization energy (IE) of the hole transporting layer (HTM) while different timescales have been reported concerning the injection of photogenerated holes from CH3NH3PbI3 even towards the same HTM. Here, we present a series of fully evaporated devices employing HTMs with different IEs. The V_oc of the devices along with the processes of hole injection and trapping are studied in terms of ideality factors and fs-transient absorption (TA) spectroscopy. We prove that the V_oc is mainly determined by the bulk and surface recombination rather than by the energetic offset between the valence band (VB) of the perovskite and the IE of the HTM. Furthermore, we find that hole injection competes with carrier thermalization and takes place from hot states in the VB independently of the IE of the HTMs. Finally, the observed difference in the timescale between hole injection and interfacial trapping is found to contribute to the high efficiency of the studied HTMs when employed in solar cell devices. Our results provide an understanding of the origin of the V_oc and point to other crucial factors that should be considered when searching for novel HTMs rather than their IE.

[1] N. Droseros et al., APL Mater., 2019, 7, 041115
[2] Dänekamp et al., J. Mater. Chem. C, 2019,7, 523-527