Enhancement of Charge Transfer in TiO2/BiOI Heterojunction Using BiFeO3 as Interface Modifier for Photoelectrochemical Conversion

The solution-processed TiO2/BiFeO3/BiOI ternary heterojunction with cascade energy level alignments was developed for photoelectrochemical conversion, in which, BiOI was deposited on BiFeO3 sensitized TiO2 mesoporous film by spin-coating method. BiFeO3 as ferroelectric material was served here as a mediator for improvement of charge separation and transfer. The photocurrent generation in TiO2/BiFeO3/BiOI sample are very stable, even measured after 50 light on/off cycles with 2000s. Moreover, compared with the TiO2/BiOI film, TiO2/BiFeO3/BiOI film showed about twice as high photocurrent density and photocatalytic activity. Kelvin probe force microscope showed that the surface potential of TiO2/BiFeO3/BiOI film was 0.456 V, which was obviously larger than 0.226 V in TiO2/BiOI sample. The increased surface potential should be originated from the polarization electric-field Eself by BiFeO3 interlayer, in which the direction of electric-field was supposed to be directed toward the BiOI. The presence of Eself consequently resulted in the better dissociation of photo-generated electrons and holes. Charge transport dynamics suggested that charge transfer rate increased from 6.813 s-1 of TiO2/BiOI heterojunction to 22.280 s-1 of TiO2/BiFeO3/BiOI heterojunction, and surface charge recombination rate reduced from 10.305 s-1 of the TiO2/BiOI to 7.707 s-1 of TiO2/BiFeO3/BiOI heterojunction, which results in the enhanced photoelectrochemical conversion in TiO2/BiFeO3/BiOI heterojunction.

Synergetic Effect of Different Carrier Dynamics in Pm6:Y6:ITIC-M Ternary Cascade Energy Level System

Although reported ternary polymer solar cells have higher power conversion efficiency than binary polymers, the mechanism of exciton separation and charge transport in this complex ternary system is still unclear. Herein, based on PM6:Y6:ITIC-M ternary solar cells, we combine the technique of luminescence spectroscopy, including electroluminescence (EL) and photoluminescence (PL) with photovoltaic measurements, to understand clearly the detailed roles of ITIC-M as the third component in the contribution of device performance. The results show that ITIC-M can form the alloy-like composite with Y6 but leave individual Y6 acceptor to conduct charge transfer with PM6 donor, which improves Voc but decreases Jsc because of poor charge transfer capacity of ITIC-M. Meanwhile, the energy transfer from PM6 to ITIC-M exists in the active layers; small IE suppresses exciton dissociation. Deteriorating performance of solar cells demonstrates that, except for complementary absorption spectrum and suitable energy levels in PM6:Y6:ITIC-M system, the synergetic effects of carrier dynamics among different organic materials play an important role in influencing the performance of ternary solar cells.

Morphology Optimization of Perovskite Films for Efficient Sky-Blue Light Emitting Diodes via a novel Green Anti-Solvent Dimethyl Carbonate

Quasi-two-dimensional (quasi-2D) perovskites have been identified as promising emitters for high-efficiency blue PeLEDs, attributed to efficient radiative recombination resulted from the cascade energy transfer from low-n phases to high-n phases....