Photocurrent in Metal-Halide Perovskite/Organic Semiconductor Heterostructures: Impact of Microstructure on Charge Generation Efficiency

Hybrid organic-inorganic metal-halide perovskites have emerged as versatile materials for enabling low-cost, mechanically flexible optoelectronic applications. The progress has been commendable; however, technological breakthroughs have outgrown the basic understanding of processes occurring in bulk and at device interfaces. Here, we investigated the photocurrent at perovskite/organic semiconductor interfaces in relation to the microstructure of electronically active layers. We found that the photocurrent response is significantly enhanced in the bilayer structure as a result of a more efficient dissociation of the photogenerated excitons and trions in the perovskite layer. The increase in the grain size within the organic semiconductor layer results in reduced trapping and further enhances the photocurrent by extending the photocarriers' lifetime. The photodetector responsivity and detectivity have improved by 1 order of magnitude in the optimized samples, reaching values of 6.1 ± 1.1 A W^-1, and 1.5 × 10¹¹ ± 4.7 × 10¹⁰ Jones, respectively, and the current-voltage hysteresis has been eliminated. Our results highlight the importance of fine-tuning film microstructure in reducing the loss processes in thin-film optoelectronics based on metal-halide semiconductors and provide a powerful interfacial design method to consistently achieve high-performance photodetectors.

Structural Diversity in 2,2'-[Naphthalene-1,8:4,5-bis(dicarboximide)-N,N'-diyl]-bis(ethylammonium) Iodoplumbates

Crystallization from solutions containing 2,2'-[naphthalene-1,8:4,5-bis(dicarboximide)-N,N'-diyl]-bis(ethylammonium) diiodide ((NDIC2)I₂) and PbI₂ has been investigated. Eight different materials are obtained, either by variation of crystallization conditions or by subsequent thermal or solvent-induced transformations. Crystal structures have been determined for five materials. [(NDIC2)₂Pb₅I₁₄(DMF)₂]·4DMF (DMF = N,N-dimethylformamide) (1), [(NDIC2)Pb₄I₁₀]·4DMF (3), [(NDIC2)Pb₂I₆]·4NMP (NMP = N-methyl-2-pyrrolidone) (4), and [(NDIC2)Pb₂I₆]·2H₂O (5) form 1-dimensional (1D) chains consisting of PbI₆ (and, in the case of 1, PbI₅(DMF)) octahedra, either solely face-sharing or a mixture of face-sharing and vertex-sharing. The structure of [(NDIC₂)₃Pb₅I₁₆]·6NMP (2) contains 0D clusters; these consist of three PbI₆ octahedra and two unusually coordinated lead centers that exhibit three relatively short Pb-I bonds, two very long Pb-I contacts, and η²-coordination of an aromatic ring of NDIC2 to the lead. Close contacts between iodide ions and the imide rings of NDIC2 in four of the structures suggest that an iodide-to-NDIC2 charge-transfer interaction may be responsible for the observed red coloration of the materials. The optical and electrical properties of 1 have been studied; its onset of absorption is at 2.0 eV, and its conductivity was measured as 5.4 × 10^-5 ± 1.1 × 10^-5 S m^-1.