We investigate the effects of （N,N’-diphenyl）-N,N’-bis（1-naphthyl）-1,1’-biphenyl-4,4’-diamine （NPB） buffer layers on charge collection in inverted ZnO/MEH-PPV hybrid devices. The insertion of a 3-nm NPB thin layer enhances the efficiency of charge collection by improving charge transport and reducing the interface energy barrier, resulting in better device performances. S-shaped light J–V curve appears when the thickness of the NPB layer reaches 25 nm, which is induced by the inefficient charge extraction from MEH-PPV to Ag. Capacitance–voltage measurements are performed to further investigate the influence of the NPB layer on charge collection from both simulations and experiments.
The ZnO quantum dots（QDs） were synthesized with improved chemical solution method.The size of the ZnO QDs is exceedingly uniform with a diameter of approximately 4.8 nm,which are homogeneously dispersed in ethanol.The optical absorption edge shifts from 370 nm of bulk material to 359 nm of QD materials due to the quantum size effect,while the photoluminescence peak shifts from 375 nm to 387 nm with the increase of the density of ZnO QDs.The stability of ZnO QDs was studied with different dispersion degrees at 0？C and at room temperature of 25？C.The agglomeration mechanisms and their relationship with the emission spectra were uncovered for the first time.With the ageing of Zn O QDs,the agglomeration is aggravated and the surface defects increase,which leads to the defect emission.
The effects of MoO3thin buffer layer on charge carrier injection and extraction in inverted configuration ITO/ZnO/MEH-PPV(poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene))/MoO3(0,5 nm)/Ag hybrid solar cells are investigated by capacitance–voltage measurement under dark and light illumination conditions.The efficiency of charge carrier injection and extraction is enhanced by inserting 5 nm MoO3thin layer,resulting in better device performances.Charge carrier transport of the whole device is improved and the interface energy barrier is reduced by inserting 5 nm MoO3thin buffer layer.The device fill factor is increased from 54.1%to 57.5%after modifying 5 nm MoO3.Simulations and experimental results consistently show that in the forward voltage under dark,the device with the 5 nm MoO3thin layer modification generates larger value of capacitance than the device without MoO3layer.While under illumination,the device with the 5 nm MoO3layer generates smaller value of capacitance than the device without the 5 nm MoO3layer in the bias region of reverse and before the peak position of maximum capacitance(VCmax).The underlying mechanism of the MoO3anode buffer layer on device current density–voltage characteristics is discussed.
Wei GongZheng XuSuling ZhaoXiaodong LiuXing FanQianqian YangChao Kong
