To date, the improvement of open-circuit voltage (V OC ) offers a breakthrough for the performance of perovskite solar cells (PSCs) toward their theoretical limit. Surface modification through organic ammonium halide salts (e.g., phenethylammonium ions PEA + and phenmethylammonium ions PMA + ) is one of the most straightforward strategies to suppress defect density, thereby leading to improved V OC . However, the mechanism underlying the high voltage remains unclear. Here, polar molecular PMA + is applied at the interface between perovskite and hole transporting layer and a remarkably high V OC of 1.175 V is obtained which corresponds to an increase of over 100 mV in comparison to the control device. It is revealed that the equivalent passivation effect of surface dipole effectively improves the splitting of the hole quasi-Fermi level. Ultimately the combined effect of defect suppression and surface dipole equivalent passivation effect leads to an overall increase in significantly enhanced V OC . The resulted PSCs device reaches an efficiency of up to 24.10%. Contributions are identified here by the surface polar molecules to the high V OC in PSCs. A fundamental mechanism is suggested by use of polar molecules which enables further high voltage, leading ways to highly efficient perovskite-based solar cells.
Surface defect passivation through additional molecular bonding plays a crucial role in optimization of perovskite-based photovoltaic devices. So far, quantization of the defect site coverage by molecular passivation remains unclear from a macroscopic view. We herein unravel the coverage possibility of the surface defect sites of perovskite films by the added molecule passivators upon an MAPbI3 perovskite system. Concerns of inconsistent time-resolved photoluminescence (TRPL) spectroscopic measurements are dispelled by vapor-deposition fabrications of highly uniform perovskite films. The surface defect densities of perovskite films are derived from global fittings of the charge carrier dynamics to the measured TRPL decays. It is revealed the Langmuir adsorption relationship of the defect site coverage with respect to the added amount of tri-n-octylphosphine oxide passivation molecules. Our work supplements the dynamical bonding model of the molecular passivation process and provides reliable knowledge upon the bonding process between molecules and defects, which leads to rationalized surface passivation methodologies in perovskite photovoltaics communities.
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