Decreased Charge Transport Barrier and Recombination of Organic Solar Cells by Constructing Interfacial Nanojunction with Annealing-Free ZnO and Al Layers

To overcome drawbacks of the electron transport layer, such as complex surface defects and unmatched energy levels, we successfully employed a smart semiconductor–metal interfacial nanojunciton in organic solar cells by evaporating an ultrathin Al interlayer onto annealing-free ZnO electron transport layer, resulting in a high fill factor of 73.68% and power conversion efficiency of 9.81%. The construction of ZnO-Al nanojunction could effectively fill the surface defects of ZnO and reduce its work function because of the electron transfer from Al to ZnO by Fermi level equilibrium. The filling of surface defects decreased the interfacial carrier recombination in midgap trap states. The reduced surface work function of ZnO-Al remodulated the interfacial characteristics between ZnO and [6,6]-phenyl C71-butyric acid methyl ester (PC₇₁BM), decreasing or even eliminating the interfacial barrier against the electron transport, which is beneficial to improve the electron extraction capacity. The filled surface defects and reduced interfacial barrier were realistically observed by photoluminescence measurements of ZnO film and the performance of electron injection devices, respectively. This work provides a simple and effective method to simultaneously solve the problems of surface defects and unmatched energy level for the annealing-free ZnO or other metal oxide semiconductors, paving a way for the future popularization in photovoltaic devices

Mechanism of Polyfluorene Interlayer in Ultraviolet Photodetector: Barrier-Blocking Electron Transport and Light-Inducing Hole Injection

A remarkable performance ultraviolet (UV) photodetector was demonstrated by introducing a poly­(9,9-dihexylfluorene) (PDHF) interlayer with the roles of barrier-blocking electron transport and light-inducing hole injection, leading to enhanced properties of the device both in dark and under UV illumination. The PDHF interlayer can efficiently block the electrons, which provides low dark current as well as the reduced noise for devices. Furthermore, the accumulation of photogenerated electrons causes the energy-band bending, leading to promoted gain of holes under UV illumination. The specific detectivity of the device with the PDHF interlayer reaches 1.86 × 10¹³ cm Hz^1/2 W^–1. Moreover, the response and recovery speed have been upgraded due to the improvement of the carrier transport mechanism

Boosted Electron Transport and Enlarged Built-In Potential by Eliminating the Interface Barrier in Organic Solar Cells

A smart interface modification strategy was employed to simultaneously improve short-circuit current density (<i>J</i>_sc) and open-circuit voltage (<i>V</i>_oc) by incorporating a poly­[(9,9-bis­(3′-(<i>N</i>,<i>N</i>-dimethylamion)­propyl)-2,7-fluorene)-<i>alt</i>-2,7-(9,9-dioctyl)-fluorene] (PFN) interlayer between a TiO₂ film and an active layer, arising from the fact that PFN effectively eliminated the interface barrier between TiO₂ and the fullerene acceptor. The work function (WF) of TiO₂ was apparently reduced, which facilitated effective electron transfer from the active layer to the TiO₂ electron transport layer (ETL) and suppressed charge carrier recombination between contact interfaces. Electron injection devices with and without a PFN interlayer were fabricated to prove the eliminated electron barrier, meanwhile photoluminescence (PL) and time-resolved transient photoluminescence (TRTPL) were measured to probe much easier electron transfer from [6,6]-phenyl C71-butyric acid methyl ester (PC₇₁BM) acceptor to TiO₂ ETL, contributing to enhanced <i>J</i>_sc. The shift in vacuum level altered the WF of PC₇₁BM, which enlarged the internal electrical field at the donor/acceptor interface and built-in potential (<i>V</i>_bi) across the device. Dark current characteristics and Mott–Schottky measurements indicated the enhancement of <i>V</i>_bi, benefiting to increased <i>V</i>_oc. Consequently, the champion power conversion efficiency for a device with a PFN interlayer of 0.50 mg/mL reached to 7.14%, which is much higher than the PCE of 5.76% for the control device

Gas Sensors Based on Metal Sulfide Zn_1–<i>x</i>Cd_<i>x</i>S Nanowires with Excellent Performance

Metal sulfide Zn_1–<i>x</i>Cd_<i>x</i>S nanowires (NWs) covering the entire compositional range prepared by one step solvothermal method were used to fabricate gas sensors. This is the first time for ternary metal sulfide nanostructures to be used in the field of gas sensing. Surprisingly, the sensors based on Zn_1–<i>x</i>Cd_<i>x</i>S nanowires were found to exhibit enhanced response to ethanol compared to those of binary CdS and ZnS NWs. Especially for the sensor based on the Zn_1–<i>x</i>Cd_<i>x</i>S (x = 0.4) NWs, a large sensor response (<i>s</i> = 12.8) and a quick rise time (2 s) and recovery time (1 s) were observed at 206 °C toward 20 ppm ethanol, showing preferred selectivity. A dynamic equilibrium mechanism of oxygen molecules absorption process and carrier intensity change in the NWs was used to explain the higher response of Zn_1–<i>x</i>Cd_<i>x</i>S. The reason for the much quicker response and recovery speed of the Zn_1–<i>x</i>Cd_<i>x</i>S NWs than those of the binary ZnS NWs was also discussed. These results demonstrated that the growth of metal sulfide Zn_1–<i>x</i>Cd_<i>x</i>S nanostructures can be utilized to develop gas sensors with high performance

Self-Stabilized Quasi-2D Perovskite with an Ion-Migration-Inhibition Ligand for Pure Green LEDs

Perovskite light-emitting diodes (PeLEDs) have recently achieved a great breakthrough in external quantum efficiency (EQE). However, the operational stability of pure primary color PeLEDs lags far behind because of serious ion migration. Herein, a self-stabilized quasi-2D perovskite is constructed with a strategically synthesized ion-migration-inhibition ligand (IMIligand) to realize highly stable and efficient pure green PeLEDs approaching the standard green light of Rec. 2020. The IMIligand takes the role to not only eliminate migration pathways and anchor halide ions to suppress the ion migration but to also further enhance the crystalline orientation and energy transfer in quasi-2D perovskites. Meanwhile, the self-stabilized quasi-2D perovskite overcomes the degradation of electrical performance caused by conventional exogenous passivation additives. Ultimately, the figure of merit of the pure green quasi-2D PeLEDs is at least double that of previous works. The devices achieve an EQE of 26.2% and operational stability of 920 min at initial luminance of 1000 cd m–2