Porphyrinic Metal–Organic Framework Quantum Dots for Stable n–i–p Perovskite Solar Cells

As the power-conversion efficiency (PCE) of organic–inorganic lead halide perovskite solar cells (PSCs) is approaching the theoretical maximum, the most crucial issue concerns long-term ambient stability. Here, the application of PCN-224 quantum dots (QDs) is reported, a typical Zr-based porphyrinic metal–organic framework (MOF), to enhance the ambient stability of PSCs. PCN-224 QDs with abundant Lewis-base groups (e.g., CO, C−N, CN) contribute to high-quality perovskite films with enlarged grain size and reduced defect density by interaction with under-coordinated Pb²⁺. Meanwhile, PCN-224 QDs enable the well-matched energy level at the perovskite/hole transport layer (HTL) interface, thereby facilitating hole extraction and transport. More importantly, PCN-224 QDs-treated HTL can capture Li⁺ from bis(trifluoromethanesulfonyl)imide additive, leading to the reduced aggregation and less direct contact with moisture for hygroscopic Li-TFSI. Moreover, PCN-224 QDs mitigated Li⁺ ion migration into the perovskite layer, thus avoiding the formation of deleterious defects. The resultant devices yield a champion PCE of 22.51%, along with substantially improved durability, including humidity, thermal and light soaking stabilities. The findings provide a new approach toward efficient and stable PSCs by applying MOF QDs.     

Stabilization of α-phase FAPbI3 via Buffering Interfacial Region for Efficient p–i–n Perovskite Solar Cells

Formamidinium lead triiodide (FAPbI₃) with an ideal bandgap and good thermal stability has received wide attention and achieved a record efficiency of 26% in n–i–p (regular) perovskite solar cells (PSCs). However, imperfect FAPbI₃ formation on the typical hole transport layer (HTL), high interfacial trap-state density, and unfavorable energy alignment between the HTL and FAPbI₃ result in the inferior photovoltaic performance of p–i–n (inverted) PSCs with FAPbI₃ absorber. Herein, the α-phase FAPbI₃ is stabilized by constructing a buffer interface region between the NiO_x HTL and FAPbI₃, which not only diminishes NiO_x/FAPbI₃ interfacial reactions and defects but also facilitates carrier transport. Upon the construction of a buffer interface region, FAPbI₃ inverted PSC exhibits a high-power conversion efficiency of 23.56% (certified 22.58%) and excellent stability, retaining 90.7% of its initial efficiency after heating at 80 °C for 1000 h and 84.6% of the initial efficiency after operating at the maximum power point under continuous illumination for 1100 h. Besides, as a light-emitting diode device, the FAPbI₃ inverted PSC can be directly lit with an external quantum efficiency of 1.36%. This study provides a unique and efficient strategy to advance the application of α-phase FAPbI₃ in inverted PSCs.     

Manifestation of Flexible p–i–n Solar Cells Fabricated Using HWCVD in WSN Application

Wireless Personal Communications - The wireless sensor network (WSN) consist of battery-powered sensor nodes which are self-configured and are deployed for monitoring several physical or...     

Dual Sub-Cells Modification Enables High-Efficiency n–i–p Type Monolithic Perovskite/Organic Tandem Solar Cells

Monolithic perovskite/organic tandem solar cells (POTSCs) have attracted increasing attention owing to ability to overcome the Shockley–Queisser limit. However, compromised sub-cells performance limits the tandem device performance, and the power conversion efficiency (PCE) of POTSCs is still lower than their single-junction counterparts. Therefore, optimized sub-cells with minimal energy loss are desired for producing high-efficiency POTSCs. In this study, an ionic liquid, methylammonium acetate (MAAc), is used to modify wide-bandgap perovskite sub-cells (WPSCs), and bathocuproine (BCP) is used to modify small-bandgap organic solar cells. The Ac⁻ group of MAAc can effectively heal the Pb defects in the all-inorganic perovskite film, which enables a high PCE of 17.16% and an open-circuit voltage (V_oc) of 1.31 V for CsPbI_2.2Br_0.8-based WPSCs. Meanwhile, the BCP film, inserted at the ZnO/organic bulk-heterojunction (BHJ) interface, acts as a space layer to prevent direct contact between ZnO and the BHJ while passivating the surface defects of ZnO, thereby mitigating ZnO defect-induced efficiency loss. As a result, PM6:CH1007-based SOSCs exhibit a PCE of 15.46%. Integrating these modified sub-cells enable the fabrication of monolithic n–i–p structured POTSCs with a maximum PCE of 22.43% (21.42% certified), which is one of the highest efficiencies in such type of POTSCs.     

Structural Tailoring the Phenylenediamine Isomers to Obtain 2D Dion–Jacobson Tin Perovskite Solar Cells with Record Efficiency

2D Dion–Jacobson (DJ) tin halide perovskite shows impressive stability by introducing diamine organic spacer. However, due to the dielectric confinement and uncontrollable crystallization process, 2D DJ perovskite usually exhibits large exciton binding energy and poor film quality, resulting in unfavorable charge dissociation, carrier transport and device performance. Here, the ortho-, meta-, and para-isomers of phenylenediamine (PDA) are designed for 2D DJ tin halide perovskites. Theoretical simulation and experimental characterizations demonstrate that compared with p-PDA and m-PDA, o-PDA shows larger dipole moment, which further reduces the exciton binding energy for the 2D perovskites. Besides, there is a strong hydrogen bond interaction between o-PDA cation and inorganic octahedron, which not only improves the structural stability, but also induces larger aggregates in the precursor to form dense and uniform high-quality films, and strengthens the antioxidant barrier. More interestingly, femtosecond transient absorption further proves that o-PDA organic spacers can reduce unfavorable small n-phases, resulting in sufficient and effective charge transfer between different n-value. As a result, the 2D DJ (o-PDA)FA₃Sn₄I₁₃ solar cells achieve a record power conversion efficiency of 7.18%. The study furnishes an effective method to optimize the carrier transport and device performance by tailoring the chemical structure of organic spacers.     

Impact of 2D Ligands on Lattice Strain and Energy Losses in Narrow-Bandgap Lead–Tin Perovskite Solar Cells

Mixed lead and tin (Pb/Sn) hybrid perovskites exhibit a great potential in fabricating all-perovskite tandem devices due to their easily tunable bandgaps. However, the energy deficit and instability in Pb/Sn perovskite solar cells (PSCs) constrain their practical applications, which renders defect passivation engineering indispensable to develop highly efficient and long-term stable PSCs. Herein, the mechanisms of strain tailoring and defect passivation in Pb/Sn PSCs by 2D ligands are investigated. The 2D ligands include electroneutral cations with long alkyl chain (LAC), iodates with relatively short alkyl chain (SAC) and their mixtures. This study reveals that LAC ligands facilitate the relaxation of tensile strain in perovskite films while SAC ligands cause strain buildup. By mixing LAC/SAC ligands, tensile strain in perovskite films can be balanced which improves solar cell performance. PSCs with admixed β-guanidinopropionic acid (GUA)/phenethylammonium iodide (PEAI) exhibit enhanced open circuit voltage and fill factor, which is attributed to reduced nonradiative recombination losses in the bulk and at the interfaces. Furthermore, the operational stability of PSCs is slightly improved by the mixed 2D ligands. This work reveals the mechanisms of 2D ligands in strain tailoring and defect passivation toward efficient and stable narrow-bandgap PSCs.     

A study of the i/p interface for flexible n–i–p a-Si:H thin film solar cells

In this paper, the influence of i/p interface buffer layer on the performance of flexible n–i–p a-Si:H thin film solar cells is studied. The results show that the dopant distribution in the buffer layer has large effect on the property of solar cells. A larger open circuit voltage and fill factor can be obtained when methane is introduced into the chamber prior to diborane during the deposition of buffer layer. The AMPS simulation indicates that it is beneficial to improve the built-in electric field in the i layer when the carbon is doped prior to boron, thus the carrier transport properties are improved. By further optimizing the deposition parameter, an initial conversion efficiency of 5.668% is achieved for the a-Si:H thin film solar cells on the PI substrates at 150 °C.     

Dual Role of Cu-Chalcogenide as Hole-Transporting Layer and Interface Passivator for p–i–n Architecture Perovskite Solar Cell

Inorganic hole-transport layers (HTLs) are widely investigated in perovskite solar cells (PSCs) due to their superior stability compared to the organic HTLs. However, in p–i–n architecture when these inorganic HTLs are deposited before the perovskite, it forms a suboptimal interface quality for the crystallization of perovskite, which reduces device stability, causes recombination, and limits the power conversion efficiency of the device. The incorporation of an appropriate functional group such as sulfur-terminated surface on the HTL can enhance the interface quality due to its interaction with perovskite during the crystallization process. In this work, a bifunctional Al-doped CuS film is wet-deposited as HTL in p–i–n architecture PSC, which besides acting as an HTL also improves the crystallization of perovskite at the interface. Urbach energy and light intensity versus open-circuit voltage characterization suggest the formation of a better-quality interface in the sulfide HTL–perovskite heterojunction. The degradation behavior of the sulfide-HTL-based perovskite devices is studied, where it can be observed that after 2 weeks of storage in a controlled environment, the devices retain close to 95% of their initial efficiency.     

The Diagram of p–n Junction Formed on the n-GaAs Surface by 1.5 keV Ar+ Ion Beam

Semiconductors - The core-level and valence band electronic structure of the n-GaAs (100) has been studied by synchrotron-based high-resolution photoelectron spectroscopy after irradiation by an...     

J–V Characteristic of p–n Structure Formed on n-GaAs Surface by Ar+ Ion Beam

Semiconductors - A highly defective ~10-nm-thick layer was fabricated in a high vacuum by 2.5 keV Ar+ ion bombardment of the n-GaAs surface. Valence band photoelectron spectra showed a p-type...     

Development and Study of the p–i–n GaAs/AlGaAs Tunnel Diodes for Multijunction Converters of High-Power Laser Radiation

Semiconductors - The creation of connecting tunnel diodes with a peak tunneling-current density higher than the density of the short-circuit current of photoactive p–n junctions is an...     

Understanding the influence of doping in efficient phosphorescent organic light-emitting diodes with an organic p–i–n homojunction

We report on the development and detailed investigation of highly efficient p–i–n phosphorescent organic light-emitting diodes (PhOLEDs) using 4,4′-bis(carbazol-9-yl)-biphenyl (CBP) as a single organic semiconductor matrix. Following optimization of doping concentration of both the phosphorescent emitter molecule and of the p- and n-type dopants, an external quantum efficiency (EQE) of 15% and a power efficiency (PE) of 28 lm/W are realized at a luminance of 1000 cd/m². These values are comparable to the state-of-the-art for conventional complex multilayered PhOLEDs. By analyzing the device characteristics (i.e. electroluminescence spectra, the current density–voltage behavior of single carrier devices, the transient electroluminescent decay, and the impedance spectroscopy response), we find that the device performance is closely linked to the charge carrier balance in the device, which in turn is governed by the interplay of the conductivities of the doped layers and the transport of each charge carrier species within the emitting layer.     

Manipulating the Light-Matter Interaction of PtS/MoS2 p–n Junctions for High Performance Broadband Photodetection

Due to the limited carrier concentration, 2D transition metal dichalcogenides have lower intrinsic dark current, and thus, are widely studied for high performance room photodetection. However, the light-matter interaction is still unclear, thus tuning the photoexcitation and further manipulating the photodetection is a challenge. Herein, large-area PtS films are synthesized, and the growth mechanism is investigated. It is demonstrated that PtS has an orthorhombic structure and exhibits the p-type semiconducting behavior. Then, MoS₂/PtS p–n heterojunction is fabricated, and its energy diagram is discussed based on the Kelvin probe force microscopy. The contact potential difference is about 160 mV, which is much larger than previous 2D junctions facilitating the charge separation. Furthermore, the phototransistor based on MoS₂/PtS p–n heterojunction is prepared, showing broadband photoresponse from visible to near-infrared. The manipulation of an external field on photoresponse, detectivity, and rise/fall time are explored and discussed. The responsivity can reach up to 25.43 A W⁻¹, and the detectivity is 8.54 × 10¹² Jones. These results indicate that PtS film is a prospective candidate for high-performance optoelectronic devices and broaden the scope of infrared detection materials.     

Carbon and silica interlayer influence for the photocatalytic performances of spindle-like α-Fe2O3/Bi2O3 p–n heterostructures

The p–n heterojunction is an effective structure to suppress the recombination of photogenerated charge carriers due to the built-in internal electric field. Herein, we successfully synthesize a spindle-like α-Fe₂O₃/Bi₂O₃ core–shell heterostructure, in which α-Fe₂O₃ is an n-type semiconductor and Bi₂O₃ is a p-type semiconductor. In comparison with pure α-Fe₂O₃ seeds, the α-Fe₂O₃/Bi₂O₃ p–n heterojunction photocatalyst exhibits tremendous photocatalytic performance on the degradation of Rhodamine B (RhB) under illumination of visible light. In addition, we insert an interlayer between p–n heterostructure, similar to p–i–n heterostructure. The silicon oxide and carbon are selected as the interlayer due to its different conductivity. The as-obtained α-Fe₂O₃/C/Bi₂O₃ exhibits higher degradation rate than α-Fe₂O₃/SiO₂/Bi₂O₃. The reason is attributed to the mesoporous structure of carbon layer and its high conductivity so that the photogenerated electrons can be easily transferred from the conduction band of α-Fe₂O₃ to the conduction band of Bi₂O₃ thereby promoting an effective separation of photogenerated electrons and holes. However, the introduction of interlayer reduces the photocatalytic activity due to the alteration of internal built-in electric field in the heterojunction. We envision that these results have potential applications for designing the heterostructural photocatalysts.