Mechanical and Ionic Characterization for Organic Semiconductor-Incorporated Perovskites for Stable 2D/3D Heterostructure Perovskite Solar Cells

Abstract

Hybrid metal halide perovskite (MHP) materials, while being promising for photovoltaic technology, also encounter challenges related to material stability. Combining 2D MHPs with 3D MHPs offers a viable solution, yet there is a gap in the understanding of the stability among various 2D materials. The mechanical, ionic, and environmental stability of various 2D MHP ligands are reported, and an improvement with the use of a quater-thiophene-based organic cation (4TmI) that forms an organic-semiconductor incorporated MHP structure is demonstrated. It is shown that the best balance of mechanical robustness, environmental stability, ion activation energy, and reduced mobile ion concentration under accelerated aging is achieved with the usage of 4TmI. It is believed that by addressing mechanical and ion-based degradation modes using this built-in barrier concept with a material system that also shows improvements in charge extraction and device performance, MHP solar devices can be designed for both reliability and efficiency.

Keywords: 2D materials; conjugated cations; ionic characterization; mechanical stability; metal halide perovskites; photovoltaics; reliability.

Figure 1

a) Ligand structure of BAI, 4TmI, and Br4TmI b) Schematics of the as‐formed 2D RP phase perovskite. XRD tracking of 2D perovskite thin films for c) (BA)₂PbI₄ d) (4Tm)₂PbI₄ and e) (Br4Tm)₂PbI₄ at 85°C heating under light illumination in air (RH% = 68%). UV–vis spectra tracking of 2D perovskite thin films for f) (BA)₂PbI₄, g) (4Tm)₂PbI₄, and h) (Br4Tm)₂PbI₄ at 85 °C heating under light illumination in air (RH% = 68%).

Figure 2

a) Fracture energy of (4Tm)₂PbI₄, (Br4Tm)₂PbI₄, and (BA)₂PbI₄ 2D MHP films, compared to 3D MHPs, insets are representative sample photographs taken after measurements. b) Schematic illustration of samples and fracture propagation for fracture energy measurement using the double cantilever beam (DCB) method.

Figure 3

a) Schematic illustration of perovskite solar cell configurations and mobile ion concentration (N_o ) measurement. b) Statistics of PCE based on devices without interlayers, with BAI‐2D, with 4TmI‐2D, and with Br4TmI‐2D interlayers. Statistics are from 16 devices. c) N _o evolution under 85 °C heat exposure. d) N _o evolution under light exposure. e) Device PCE evolution under 85 °C heat exposure. f) Device PCE evolution under light exposure.