Comparative Analysis of Different Ammonium-Based Cations in 2D DJ-Type Perovskite Single Crystals for High-Performance Planar Photodetectors

In this study, 2D lead-based perovskite single crystals based on symmetric diamine 1,4-butanediamine (BDA) and asymmetric diamine N,N-dimethyl-1,3-propanediamine (DMePDA) are synthesized by a slow cooling method. Results show that DMePDAPbI4 exhibits a lower bandgap of 2.10 eV as compared to BDAPbI4 (2.22 eV), which is desirable for efficient optoelectronic detection. Structural analysis and the density functional theory (DFT) calculations show that the DMePDAPbI4 features a much larger Pb–I–Pb bond angle than that of BDAPbI4, together with a smaller effective mass of electrons and holes, thereby higher carrier mobility. Additionally, as compared to BDAPbI4, DMePDAPbI4 exhibits a higher energy of total density of states (DOSs) for the organic cations, suggesting weaker hydrogen bonding and reduced energy barrier between the inorganic layer and the organic cation. Furthermore, planar photodetectors based on single crystals are fabricated, and the detection performance of the DMePDAPbI4 device far surpasses that of BDAPbI4. This superiority is evident in terms of photoresponsivity (18.04 mA W1–) and specific detectivity (2.50 × 1010 Jones) for the DMePDAPbI4 device, which greatly exceeds the values for the BDAPbI4 device (0.15 mA W1–, 5.27 × 108 Jones). This study elucidates the design principles of photodetectors utilizing crystal structures with diverse amino groups, offering promising prospects for future 2D DJ-type perovskite single crystals.