Structural non-centrosymmetry in semiconducting organic–inorganic hybrid halide perovskites can introduce functionalities like anomalous photovoltaics and nonlinear optical properties. Here we introduce a design principle to prepare Pb- and Bi-based two- and one-dimensional hybrid perovskites with polar non-centrosymmetric space groups. The design principle relies on creating dissimilar hydrogen and halogen bonding non-covalent interactions at the organic–inorganic interface. For example, in organic cations like I–(CH2)3–NH2(CH3)+ (MIPA), −CH3 is substituted by −CH2I at one end, and −NH3 + is substituted by −NH2(CH3)+ at the other end. These substitutions of two −H atoms by −I and −CH3 reduce the rotational symmetry of MIPA at both ends, compared to an unsubstituted cation, for example, H3C–(CH2)3–NH3 +. Consequently, the dissimilar hydrogen–iodine and iodine–iodine interactions at the organic–inorganic interface of (MIPA)2PbI4 2D perovskites break the local inversion symmetries of Pb–I octahedra. Owing to this non-centrosymmetry, (MIPA)2PbI4 displays visible to infrared tunable nonlinear optical properties with second and third harmonic generation susceptibility values of 5.73 pm V–1 and 3.45 × 10–18 m2 V–2, respectively. Also, the single crystal shows photocurrent on shining visible light at no external bias, exhibiting anomalous photovoltaic effect arising from the structural asymmetry. The design strategy was extended to synthesize four new non-centrosymmetric hybrid perovskite compounds. Among them, one-dimensional (H3N–(CH2)3–NH(CH3)2)BiI5 shows a second harmonic generation susceptibility of 7.3 pm V–1 and a high anomalous photovoltaic open-circuit voltage of 22.6 V.

Hybrid lead halide perovskites and their derivatives are important optoelectronic materials but suffer from water instability. Combining both the optoelectronics and the water stability of such systems is a major challenge in material design today. To address this issue, we employ the well-known π-conjugation and cation−π interaction concepts in designing a hybrid lead halide perovskite derivative system. (4,4′-VDP)Pb2Br6 (VDP = vinylenedipyridinium) single crystals are prepared. They have a one-dimensional (1D) arrangement of inorganic Pb–Br sublattices connected via the 4,4′-VDP organic sublattice. The π-conjugation in the 4,4′-VDP sublattice allows electronic communication between the 1D Pb–Br units, reducing the band gap and improving the photoconductivity. Importantly, N+ of one 4,4′-VDP molecular ion interacts with the π-electron cloud of the adjacent one. This intermolecular cation−π interaction extends throughout the organic sublattice, making the hybrid crystal stable when stored under water for more than a year without requiring any encapsulations.

Heterostructures based on two-dimensional (2D) materials have demonstrated huge potential in various modern-day electronic and optoelectronic devices, but their optoelectronic properties are strongly influenced by the defects present in these materials. Hence, an in-depth understanding of the role of defects is vital in designing high-performance optoelectronic devices. Here, we investigated the role of defects in the electronic transport and photoresponse properties of a silicon−MoS 2 p−n junction heterostructure through temperature-dependent electrical studies and demonstrated a method for improving their photoresponse. The presence of space-charge-limited transport with exponentially distributed trap states was evident from the temperature-dependent I−V characteristics. The temperature dependence of the ideality factor and intensity-dependent photoresponse also elucidated the nature of defects. The amplitude of low-frequency 1/f noise was observed to decrease with an increase in temperature, revealing the significant influence of defects on the charge transport. These defects can often cause recombinations, diminishing the photoresponse and severely degrading the optoelectronic properties. A significant enhancement in photoresponse by reducing the recombination centers was obtained by altering the surrounding dielectric environment. For a particular dielectric, the enhancement was observed to be more prominent toward low temperatures. In addition, the surrounding dielectric also effectively suppressed the low-frequency noise levels in the heterostructure. Insights from this study would help in designing and improving the properties of low-dimensional optoelectronic devices.