Hybrid organic-inorganic perovskites have shown great promise as solar cell absorbers, achieving laboratory-condition efficiencies approaching 27%, comparable to their silicon-based counterparts.[1] However, their poor environmental stability, especially under humid conditions, remains a major barrier to commercialisation.[2] Layered (2D) perovskites offer enhanced environmental stability by incorporating large hydrophobic organic ligands in place of the small molecules used in 3D analogues. This increased stability, however, comes at the expense of reduced efficiency. Layered perovskites present high exciton binding energies in the 100s of meV, in contrast to the 7–50 meV range observed in 3D systems, such as methylammonium lead iodide (MAPbI₃), where excitons are fully dissociated at room temperature.[3]

This work investigates layered perovskites with ligands of varying composition, length, interlayer spacing and structural phase (Ruddlesden-Popper vs Dion-Jacobson), which are compared to their 3D counterpart MAPbI₃. Through temperature- and light intensity-dependent electrical measurements of perovskite thin films, we assess the role of high exciton binding energy in photocurrent generation. Results suggest that, regardless of spacer composition, excitons are fully dissociated at room temperature. Therefore, the relatively high exciton binding energy is not limiting photocurrent generation as previously suggested to explain the poor performance of pure 2D perovskite solar cell devices. Moreover, the photoconductivity of the 2D perovskites studied decreases by only one order of magnitude as the sample is cooled to 100 K. This significantly contradicts the drastic reduction in free carrier density predicted at low temperatures by the Saha equation, a model used to describe the relationship between exciton and free charge carrier population.[4] Finally, photo-Hall measurements are used to isolate the role of photogenerated charge carrier density in the photoconductivity evolution.

Our study, therefore, indicates that poor performance of 2D perovskite solar cells does not arise from suppressed photocurrent generation, which is comparable to their 3D counterparts. Further work is required to probe and understand other possible sources of limitations, including carrier recombination at interfaces, out-of-plane charge transport, and charge carrier extraction.