Multifunctional Regioisomeric Passivation Strategy for Fabricating Self-Driving, High Detectivity All-Inorganic Perovskite Photodetectors

Rationally tailored passivator with multisite surface-anchors for suppressing ion migration toward air-stable perovskite solar cells

Trap states in perovskite films fabricated using the solution method can capture photo-generated carriers, expedite ion migration, and contribute to decomposition of the perovskite layer, thereby emerging as a major threat to the commercialization of perovskite solar cells (PSCs). To address these issues, passivation of the surface traps on perovskite films via molecules with functional groups is proven to be one of the most effective tactics for obtaining high-performance PSCs. Herein, potassium nonafluoro-1-butanesulfonate (KNFBS) molecules with multiple chemical bonds, including multisite F atoms, sulfonic acid groups and K ions, were introduced as surface-anchoring passivators to improve the film quality and passivate trap states. Based on in situ conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM) results, it was found that undercoordinated Pb and I vacancy defects on the surface and grain boundaries (GBs) of perovskite films can be synergistically curtailed via multiple chemical interactions, including Lewis acid-base, hydrogen and ionic bonds. Moreover, the influence of varied ligands on defects and halide ion migration in perovskites as well as the mechanism behind it were extensively explored. Therefore, the KNFBS-treated perovskite films with a more homogeneous surface potential distribution significantly reduced point and vacancy defects and dangling bond density, facilitated charge transfer, exhibited an optimized power conversion efficiency (PCE) of 20.88% and enhanced air stability for the PSCs fabricated and stored in fully open-air conditions. The work has not only elucidated the fundamental mechanisms of ion migration and multisite passivation at the surface and GBs of perovskites but also probes into ligand design strategies for further improving the performance of perovskite photovoltaics.

Textured Perovskite/Silicon Tandem Solar Cells Achieving Over 30% Efficiency Promoted by 4-Fluorobenzylamine Hydroiodide

Monolithic textured perovskite/silicon tandem solar cells (TSCs) are expected to achieve maximum light capture at the lowest cost, potentially exhibiting the best power conversion efficiency. However, it is challenging to fabricate high-quality perovskite films and preferred crystal orientation on commercially textured silicon substrates with micrometer-size pyramids. Here, we introduced a bulky organic molecule (4-fluorobenzylamine hydroiodide (F-PMAI)) as a perovskite additive. It is found that F-PMAI can retard the crystallization process of perovskite film through hydrogen bond interaction between F- and FA+ and reduce (111) facet surface energy due to enhanced adsorption energy of F-PMAI on the (111) facet. Besides, the bulky molecular is extruded to the bottom and top of perovskite film after crystal growth, which can passivate interface defects through strong interaction between F-PMA+ and undercoordinated Pb2+/I-. As a result, the additive facilitates the formation of large perovskite grains and (111) preferred orientation with a reduced trap-state density, thereby promoting charge carrier transportation, and enhancing device performance and stability. The perovskite/silicon TSCs achieved a champion efficiency of 30.05% based on a silicon thin film tunneling junction. In addition, the devices exhibit excellent long-term thermal and light stability without encapsulation. This work provides an effective strategy for achieving efficient and stable TSCs.

Uncooled Broadband Photodetection via Light Trapping in Conformal PtTe2-Silicon Nanopillar Heterostructures

Dirac semimetals have demonstrated significant attraction in the field of optoelectronics due to their unique bandgap structure and high carrier mobility. Combining them with classical semiconductor materials to form heterojunctions enables broadband optoelectronic conversion at room temperature. However, the low light absorption of layered Dirac semimetals substantially limits the device's responsivity in the infrared band. Herein, a three-dimensional (3D) heterostructure, composed of silicon nanopillars (SiNPs) and a conformal PtTe2 film, is proposed and demonstrated to enhance the photoresponsivity for uncooled broadband detection. The light trapping effect in the 3D heterostructure efficiently promotes the interaction between light and PtTe2, while also enhancing the light absorption efficiency of silicon, which enables the enhancement of the device responsivity across a broadband spectrum. Experimentally, the PtTe2-SiNPs heterojunction device demonstrates excellent photoelectric conversion behavior across the visible, near-infrared, and long-wave infrared (LWIR) bands, with its responsivity demonstrating an order-of-magnitude improvement compared to the counterparts with planar silicon heterojunctions. Under 11 μm laser irradiation, the noise equivalent power (NEP) can reach 1.76 nW·Hz-1/2 (@1 kHz). These findings offer a strategic approach to the design and fabrication of high-performance broadband photodetectors based on Dirac semimetals.

Modulating Dimensionality of 2D Perovskite Layers for Efficient and Stable 2D/3D Perovskite Photodetectors

Two-dimensional (2D) perovskites have been widely adopted for improving the performance and stability of three-dimensional (3D) metal halide perovskite devices. However, rational manipulation of the phase composition of 2D perovskites for suitable energy level alignment in 2D/3D perovskite photodetectors (PDs) has been rarely explored. Herein, we precisely controlled the dimensionality of the 2D perovskite on CsPbI2Br films by tuning the polarity of the n-butylammonium iodide (BAI)-based solvents. In comparison to the pure n = 1 2D perovskite (ACN-BAI) formed by acetonitrile treatment, a mixture of n = 1 and n = 2 phases (IPA-BAI) generated by isopropanol (IPA) treatment guaranteed more robust defect passivation and favorable energy level alignment at the perovskite/hole transport layer interface. Consequently, the IPA-BAI PD exhibited a responsivity of 0.41 A W-1, a detectivity of 1.01 × 1013 Jones, and a linear dynamic range of 120 dB. Furthermore, the mixed-phase 2D layer effectively shielded the 3D perovskite from moisture. The IPA-BAI device retained 76% of its initial responsivity after 500 h of nonencapsulated storage at 10% relative humidity. This research provides valuable insights into the dimensional modulation of 2D perovskites for further enhancing the performance of 2D/3D perovskite PDs.