Reducing Traps Density and Carriers Concentration by Ge Additive for An Efficient Quasi 2D/3D Perovskite Solar Cell
We realize the doping of hydrophobic bulky 2D phenylethylammonium (PEA+) is desirable to stabilize perovskite matrix and enhance stability. The addition of PEA+ alters the crystal growth orientation and improves the connectivity of the crystal grains. However, solely adding the PEA+ material is capable-less to fully passivate the severe bulk recombination sites/interior defects due to Sn vacancies, led to an efficiency of 3.96% (Voc of 0.36 V) for a Ge-free device. Whilst, we find that the addition of a smaller size Ge ions; with an optimum doping concentration, has effectively reduced the leakage current and suppressed the carrier density of the perovskite. From the perspective of traps, the addition of Ge reduces traps, typically deep traps and its effectiveness (Ge) in traps passivation was further deduced from thermally stimulated current (TSC) profile. The total trap density was doubly reduced to 4.14x1020 cm-3 when 7.5 mole% Ge was added, which led to photo-conversion efficiency of 7.45% with a high Voc of 0.46 V. In addition, the defect healing by the Ge additive has significantly enhanced the stability of the un-encapsulated device for 192h. This work shows that Ge is an effective additive to suppress recombination sites (trap states passivation); leading to the establishment of an efficient tin based perovskite solar cell.