Insights into Accelerated Degradation of Perovskite Solar Cells under Continuous Illumination Driven by Thermal Stress and Interfacial Junction

Abstract

The operational stability of encapsulated halide perovskite solar cells (HaPSCs) is imperative for their commercialization. Despite improvements in device stability, we lack insights into the irreversible degradation of devices under prolonged illumination and heat stress. Here, we investigated the operational stability of devices (∼1 cm2) made with poly­(triaryl amine) (PTAA; power conversion efficiency PCE ≈ 19.32%) and sputtered NiO x (PCE ≈ 15.60%) as a hole-transport layer (HTL) under light (for >1000 h) at 20, 60, and 85 °C to unravel the degradation mechanisms. Degradation of the PTAA device was accelerated by interface deterioration and bulk decomposition initiated by the formation of voids and PbI2 via iodine migration from defective regions at the columnar grain boundaries with the release of I2 gas. The NiO x device, with its immunity to iodine and its moisture-resistive properties, had significantly improved stability with suppression of the HaP bulk degradation by alleviation of internal defect dynamics. Our results corroborate that the formation of voids and PbI2 crystallites at columnar intergrains or at the HTL (ETL) /HaP interface with the release of I2 gas is the primary cause of device degradation. Capacitance–voltage analysis showed that the PTAA device develops a much wider defective interface layer than the NiO x device, driven mainly by the chemical reaction of iodine with the interfacial layer. Thus, our results reveal that although the cracking of columnar intergrains and defective spots in the perovskite bulk is the main origin of device degradation, the nature of the carrier transport layer also partly contributes to catalyzing bulk and interface degradation. Thus, the passivation of columnar intergrain defects in the HaP bulk and lamination of the interface with a chemically inert to iodine and a moisture-resistive carrier-selective layer is crucial to the operational stability of HaPSCs.

Interfacial Embedding for High‐Efficiency and Stable Methylammonium‐Free Perovskite Solar Cells with Fluoroarene Hydrazine

“…[1,2] However, this has imposed challenges for its practical application due to its lacking stability under heat and light stress as well as susceptibility to a humid atmosphere. [3][4][5][6] The surface passivation approach has been widely employed in PSCs to improve the device parameters as well as stability as a consequence of mitigating the defect activities, [7] modifying interfacial band alignments, [8] improving carrier extraction dynamics, [9] and enhancing moisture tolerability. [10,11] Several functional molecules have been employed for passivating materials at the interfaces [12,13] or additives in the perovskite precursor solution.…”

Enhancing operational stability in perovskite solar cells by solvent-free encapsulation method

“…2a, encapsulated samples present better stability when samples are exposed to temperatures above the phase transition/ionic migration. Previous studies 45,46 have indicated the tendency of methylammonium iodide to be removed from the crystal structure when the temperature exceeds 400 K. The temperature dependence of the bandgap of the perovskite semiconductor compound is extracted and shown in Fig. 2e and f.…”

Pseudohalide Functional Additives in Tin Halide Perovskite for Efficient and Stable Pb-Free Perovskite Solar Cells

“…To gain insight into the defect densities, we further studied the capacitance characteristics of the device to study the impact of additives on the carrier profile. The capacitance response accounts for the carrier distribution (free carrier and defect density) − and ion or charge accumulation at the interface in thin-film solar cells. The capacitance–frequency ( C–f ) response (Figure S11) for the pristine device shows a slightly larger value in the range of 1 to 50 kHz that stems from the absorber layer.…”