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The piezo-phototronic effect, as an effective interfacial regulating strategy, utilizes piezoelectric polarization charges present at the local junction/interface to modulate the optoelectronic processes of charge carrier such as generation, separation, transport and recombination, which is in close relationship with crystal orientation of the piezoelectric semiconductors. In this work, the piezo-phototronic effect is utilized to modulate the photoresponse performances of a -axis GaN microwire/p-polymer inorganic/organic hybrid photosensor. The output photocurrent experiences an increase followed by a decrease as increasing compressive strain, while it decreases monotonously as increasing tensile strain, resulting in a maximum values at each light intensity under a certain compressive strain. Besides, the modulation of photoresponse by the piezo-phototronic effect is more significant under weak illumination condition. By applying a −0.32% compressive strain, the sensitivity and responsivity of the hybrid photosensor are greatly enhanced by 508% and 354%, respectively. Two independent processes that affect photogenerated charge carriers separation and transport by strain are discovered, which is different from those normally investigated in c -axis hybrid nanostructures. [ABSTRACT FROM AUTHOR]

The counter electrode (CE) plays an important role in determining the overall performance of quantum dots (QDs) sensitized solar cells (QDSCs) by collecting the electrons from the external circuit and catalyzing the reduction of oxidized electrolyte. Metal sulfides/selenides have been commonly used as CE in QDSCs. Among these CEs, the copper selenides are considered to be a superior CE for realizing highly efficient QDSCs due to its excellent catalytic activity. However, there has always been a trade-off between catalytic activity and conductivity in copper selenides CEs, such as the CE based on copper selenide nanoparticles has highest specific surface areas, leading to best catalytic activity compared with the CEs based on other copper selenide nanostructures (nanowires, nanorods, nanosheets etc.). But it also faces the worst conductivity due to a large number of grain boundaries existed in the copper selenide film based on nanoparticles. In this work, graphene (GR)/Cu 2-x Se composite material has been prepared via a facile hot injection method, and their photovoltaic and electrochemical properties are studied in detail. Through optimizing the ratio of GR: Cu 2-x Se and sintering temperature, the QDSCs based on the optimized GR/Cu 2-x Se composite CE shows an obvious improvement in cell performances and yield a PCE of 6.66% compared with that of the cells based on bare Cu 2-x Se (5.95%), bare Graphene (2.82%) and bare Cu x S (4.85%) CEs. The improved performance of the composite CE was attributed to the combining effect of high catalytic activity of Cu 2-x Se nanoparticles and good conductivity of graphene. This work demonstrates that GR/Cu 2-x Se composite CE could be potential candidate for realizing high efficiency QDSCs. • Graphene (GR)/Cu 2-x Se composite material has been prepared via a facile hot injection method. • The photovoltaic and electrochemical properties of the composite material were studied in detail. • The QDSSCs based on the composite CE shows an obvious improvement in cell performances and yield a PCE of 6.66%. [ABSTRACT FROM AUTHOR]