Relation between Fluorescence Quantum Yield and Open-Circuit Voltage in Complete Perovskite Solar Cells

Bringing the V-oc of a perovskite solar cell toward its radiative value, corresponding to a 100% external fluorescence quantum yield (QY) of the cell, has been pursued to reach the highest performance photovoltaic devices. Therefore, much research has been focused on maximizing the QY of the active layer isolated from the rest of the cell layers. However, such quantity does not often correlate with the V-oc following the ideal diode relation. Herein, the QYs of complete FA(0.8)MA(0.2)PbI(3-y)Br(y) solar cells are reported, ranging from 0.1% to 3%, and compared with their V(oc)s, ranging from 1 to 1.13 V. By combining these measurements with electromagnetic simulations based on a full-wavevector detailed balance and a fluorescence power-loss model, it is demonstrated that a nonoptimal V-oc in mixed-cation lead halide perovskite cells is not only due to nonradiative photocarrier recombination at traps. In addition to the expected parasitic absorption of the emitted photons in the electrode layers, discrepancies appear between V-oc and QY. These discrepancies are attributed to the rise of energy barriers, a side effect of trap removal. Indeed, although surface passivation may enhance the QY, its beneficial effect may be counterbalanced by the emergence of such barriers between active and charge-transporting layers.