Two-dimensional Ruddlesden-Popper (2DRP) halide perovskites have emerged as promising solar absorbers due to their much-enhanced stability compared with their three-dimensional counterparts, but the light conversion efficiency is limited by their intrinsic optoelectronic properties such as increased exciton binding energy and poor cross-layer carrier transport properties. We herein demonstrate, through first-principles calculations, that the efficiency of 2DRP halide perovskites can be enhanced by adopting the short-chain interlayer spacers among perovskite layers. We adopted short-chain alkylmethylammonium (MA) and formamidinium (FA) organic cations to exchange the regular long-chain butylammonium (BA) and phenethylammonium (PEA) cations in 2DRP halide perovskites with the formula $A_{2}B{\mathrm{Pb}}_2{\mathrm{I}}_7$ ($A=\mathrm{BA}$, PEA, MA, and FA; $B=\mathrm{MA}$ and FA). We find that varying the interlayer spacers results in changed distortion of ${\mathrm{PbI}}_6$ octahedra of the perovskite framework, which in turn influences the stability and electronic structure of 2DRP perovskites. Compared with the long-chain BA/PEA intercalated 2DRP perovskites, the short-chain MA/FA intercalated ones have slightly reduced thermodynamic stability, but their calculated bandgaps are closer to the ideal value for solar cells (1.3–1.6 eV), accompanied with comparable carrier effective masses and optical absorption. More importantly, they demonstrate lower exciton binding energies and two orders of magnitude increased out-of-plane carrier tunneling probability. These factors are expected to further enhance the power conversion efficiency of 2DRP-based solar cells.

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• Electronic structure
• Optoelectronics
• Photovoltaic absorbers
• Semiconductor compounds
• Density functional calculations