Enhancing Perovskite Solar Cell Performance by Interface Engineering Using CH3NH3PbBr0.9I2.1 Quantum Dots.

To improve the interfacial charge transfer that is crucial to the performance of perovskite solar cells, the interface engineering in a device should be rationally designed. Here we have developed an interface engineering method to tune the photovoltaic performance of planar-heterojunction perovskite solar cells by incorporating MAPbBr3-xIx (MA = CH3NH3) quantum dots (QDs) between the MAPbI3 perovskite film and the hole-transporting material (HTM) layer. By adjustment of the Br:I ratio, the as-synthesized MAPbBr3-xIx QDs show tunable fluorescence and band edge positions. When the valence band (VB) edge of MAPbBr3-xIx QDs is located below that of the MAPbI3 perovskite, the hole transfer from the MAPbI3 perovskite film to the HTM layer is hindered, and hence, the power conversion efficiency decreases. In contrast, when the VB edge of MAPbBr3-xIx QDs is located between the VB edge of the MAPbI3 perovskite film and the highest occupied molecular orbital of the HTM layer, the hole transfer from the MAPbI3 perovskite film to the HTM layer is well-facilitated, resulting in significant improvements in the fill factor, short-circuit photocurrent, and power conversion efficiency.

High-performance perovskite photoanode enabled by Ni passivation and catalysis.

Lead halide perovskites have achieved phenomenal successes in photovoltaics due to their suitable bandgaps, long diffusion lengths, and balanced charge transport. However, the extreme susceptibility of perovskites to water or air has imposed a seemingly insurmountable barrier for leveraging these unique materials into solar-to-fuel applications such as photoelectrochemical conversion. Here we developed a CH3NH3PbI3-based photoanode with an ultrathin Ni surface layer, which functions as both a physical passivation barrier and a hole-transferring catalyst. Remarkably, a much enhanced photocurrent density, an unassisted photoelectrochemical conversion capability, and a substantially better stability against water have been achieved, which are exceeding most of the previously reported photoanodes as well as a similar CH3NH3PbI3-based device structure but without the Ni surface layer. Our study suggests many exciting opportunities of developing perovskite-based solar-to-fuel conversion.

Ultra-low power Hf0.5Zr0.5O2 based ferroelectric tunnel junction synapses for hardware neural network applications.

Brain-inspired neuromorphic computing has shown great promise beyond the conventional Boolean logic. Nanoscale electronic synapses, which have stringent demands for integration density, dynamic range, energy consumption, etc., are key computational elements of the brain-inspired neuromorphic system. Ferroelectric tunneling junctions have been shown to be ideal candidates to realize the functions of electronic synapses due to their ultra-low energy consumption and the nature of ferroelectric tunneling. Here, we report a new electronic synapse based on a three-dimensional vertical Hf0.5Zr0.5O2-based ferroelectric tunneling junction that meets the full functions of biological synapses. The fabricated three-dimensional vertical ferroelectric tunneling junction synapse (FTJS) exhibits high integration density and excellent performances, such as analog-like conductance transition under a training scheme, low energy consumption of synaptic weight update (1.8 pJ per spike) and good repeatability (>103 cycles). In addition, the implementation of pattern training in hardware with strong tolerance to input faults and variations is also illustrated in the 3D vertical FTJS array. Furthermore, pattern classification and recognition are achieved, and these results demonstrate that the Hf0.5Zr0.5O2-based FTJS has high potential to be an ideal electronic component for neuromorphic system applications.