We have studied four 2D layered perovskites, including OA₂PbI₄ (RP phase), ODAPbI₄ and BDAPbI₄ (DJ phase), (GA)MAPbI₄ (ACI phase), where OA is [(C _m H_2m+1)NH₃](m = 8), ODA is [NH₃(CH₂) _m NH₃](m = 8), BDA is [NH₃(CH₂) _m NH₃](m = 4), and GA is [C(NH₂)₃]; RP, DJ, and ACI means Ruddlesden-Popper, Dion-Jacobson and alternating cations in the interlayer, respectively. The temperature dependence of absorption and photoluminescence (PL) spectra have been measured. From which the average phonon energy (electron-phonon interaction strength) is analyzed as around 34 (80), 47 (184), 50 (402), and 63 (758) with the unit of meV for OA₂PbI₄, ODAPbI_4, BDAPbI₄, and (GA)MAPbI₄, respectively. Larger phonon energy indicates the involvement of more phonons in organic spacer layer, with the corresponding stronger electron-phonon interaction. Furthermore, ultrafast transient absorption spectroscopy proves that, when the excitation photon energy is serval hundred meV higher than bandgap, the excitons still are the major photoexcitations in OA₂PbI₄, but polarons are major one in ODAPbI₄, BDAPbI₄, and (GA)MAPbI₄ films, no matter the excitonic transitions dominate the absorption at their band edges. This work proves the organic spacers can regulate electron-phonon interaction then optoelectronic properties in 2D perovskites profoundly, which have implications toward future rational design for relevant devices.

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