Design of surface termination for high-performance perovskite solar cells

Abstract

The existence of high defect density in the interface region limits further promotion of perovskite photovoltaic performance and long-term stability. Surface termination of perovskite films alters the interfacial electronic states, which are responsible for the carrier dynamics and physical and chemical properties of the interface. Therefore, suitable termination design is beneficial to the photoelectric performance and operational stability. Here, guanidinium thiocyanate (GASCN) was selected to modify the surface terminations of methylamine lead iodide (MAPbI₃) perovskite films by taking advantage of its strong bonding capacity and increased hydrogen-bonding interactions with the [PbI₆]⁴⁻ octahedron. Firstly, to select an effective solvent to introduce GASCN onto the surface of MAPbI₃, multiple solvents with varied polarity were tested to carefully examine their effects on the perovskite active layer in consideration of their scouring or polar erosion effect. Secondly, the surface matrix is formed after thermal annealing due to the strong chemical bonding between GA⁺ and the perovskite surface. The strong surface bonding immobilizes the anion (I⁻) and reduces its migration, so suppressing the hysteresis behavior of the assembled device. As well, the surface matrix blocks invasion of moisture and oxygen from the atmosphere and thus improves the long-term stability of assembled devices.