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Poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) are commonly used for the fabrication of organic photovoltaics (OPV). Efficiency limitations of OPVs could be circumvented by incorporation of inorganic nanostructures into organic blends. Again, integration of organic solar cells with well-developed silicon photovoltaic technology is ultimately desirable. In the present work, GaN nanowires with diameters of 25–50 nm and two lengths (200 and 500 nm) have been grown using molecular beam epitaxy technique. Solar-grade monocrystalline silicon wafers were used as substrates for nanowire synthesis. GaN nanostructures were incorporated into P3HT:PCBM photoactive layer in order to facilitate charge transfer between P3HT:PCBM and Si. Samples with and without nanowires were compared. Addition of nanowires led to the improvement in photovoltaic performance. Open circuit voltage has risen by 72% and short circuit current density by 200%. Series resistance has decreased 50 times, and power conversion efficiency has risen 20.7 times. Additional maxima are found in photocurrent spectrum corresponding to carriers being generated near GaN absorption edge. Moreover, external quantum efficiency peaks near GaN absorption edge, indicating the formation of current transfer channel via P3HT/GaN/Si cascade heterojunction. Mechanism explaining source of abovementioned improvement is proposed.

We show that by subsequent sensitization of nanostructured ZnO photoanodes with N-719 and Rose Bengal dyes an improvement or worsening of the cell efficiency may be obtained, relating to photoanodes sensitized with N-719 dye only (JSC = 2.97 mA/cm2, VOC = 0.68 V, η = 0.99%) depending on the order in which the dyes are applied. We observe that for the case when the N-719 dye is followed by Rose Bengal an increase in efficiency, short circuit current and open circuit voltage is observed (JSC = 3.95 mA/cm2, VOC = 0.71 V, η = 1.26%), which we relate to the cascade band alignment of the ZnO and the dyes. In the case when Rose Bengal is first on ZnO followed by N-719, a lowering of all parameters is observed (JSC = 2.86 mA/cm2, VOC = 0.64 V, η = 0.94%) due to the trap band alignment. Electrochemical impedance spectroscopy measurements and modelling confirmed this theory showing longer electron lifetimes in the photoanode for the cascade band alignment, enhancing electron-hole separation, than for the trap alignment, facilitating electron-hole recombination.

n-CdTe/p-CdMnTe/p-GaAs diluted magnetic diode was grown by molecular beam epitaxy technology. The forward- and reverse-bias capacitance–voltage (C–V), conductance–voltage (G–V), series resistance–voltage (R s–V), impedance–voltage (Z–V), and phase–voltage (θ–V) characteristics of this diode have been analyzed in the frequency range of 5 kHz to 1 MHz at room temperature. Both the density of interface states (N ss) and series resistance (R s) are strongly frequency dependent and decrease with increasing frequency. The values of the built-in potential ( $$ V_{\rm{bi}} $$ ), the doping concentration ( $$ N_{\rm{d}} $$ ), and the barrier height ( $$ \varphi_{{{\rm{b}}(C - V)}} $$ ) of the diode were calculated at different frequencies. Our experimental results revealed that both the series resistance and interface state density must be taken into account in studying the impedance spectroscopy on heterojunction diodes to understand their performance for electronic and optoelectronic applications. Diluted magnetic semiconductors are promising materials for future technology.

High quality n-(CdMgTe:I/n-CdTe:I)/(p-CdTe:N/p-ZnCdTe:N/p-ZnTe:N)/p-GaAs heterojunction diodes have been fabricated by molecular beam epitaxial growth. The illumination effect on the complex impedance and conductivity of heterostructure diode was investigated. The illumination intensities were taken up to the 200 mW/cm2 with frequency range of 42 Hz to 1 MHz. The observed real and imaginary parts of the complex impedance were strongly dependent on the illumination frequency. The inverse relation was observed between the illumination intensity and the complex impedance. The relaxation mechanism of the diode was analyzed by the Cole–Cole plots. The radius of the Cole–Cole curve decreases with increasing illumination intensity. This suggests a mechanism of illumination dependent on the relaxation process. It is also found that the conductivity increases linearly with increasing the illumination intensity. We can conclude that the new design heterostructure diode in our work is a good candidate in photodetector and optoelectronic applications.