Hybrid organic–inorganic self-powered photodetectors with three different configurations were fabricated and their optoelectronic performance was determined. Si is the inorganic active layer and the transparent conductor poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is the organic layer. The basic photodetector structure under study is Au/PEDOT:PSS/Si/Al. This device shows high responsivity under low irradiation levels, as well as a wideband response in the visible and near-infrared wavelength ranges. To improve the performance of this basic device, its structure was modified by the addition of a nanostructured porous silicon (PSi) layer on top of the Si substrate. The resulting Au/PEDOT:PSS/PSi/Si/Al devices have been found to show improved photoresponse under high irradiation levels together with narrowband spectral responsivity in the infrared region. To further improve the optoelectronic performance of the photodetectors, Si + PSi micro-arrays were used instead of single PSi layers, leading to devices with the structure Au/PEDOT:PSS/(Si + PSi micro-arrays)/Si/Al. These devices possess a much improved performance, showing a responsivity of 1172.87 mA W⁻¹, a specific detectivity of 5.81 × 10¹³ Jones, and a fast response speed of 396/412 μs at 0 V bias under white-light illumination (100 μW). Furthermore, a broadband spectral responsivity was achieved, with a maximum value of 473 mA W⁻¹ at 853 nm. This improved behavior is associated with the combined effect of an effective reduction of the reflectance due to the presence of PSi and an improvement of the electrical conduction given by the presence of heavily-doped Si regions.

The accurate determination of the electrical properties of photovoltaic devices is of utmost importance to predict and optimize their overall optoelectronic performance. For example, the minority carrier lifetime and the carrier diffusion length have a strong relationship with the carrier recombination rate. Additionally, parasitic resistances have an important effect on the fill factor of a solar cell. Within this context, the alternating current (AC) and direct current (DC) electrical characteristics of Si-based metal–insulator–semiconductor (MIS) Schottky barrier diodes with the basic structure Al/Si/TiO₂/NiCr were studied, aiming at using them as photovoltaic devices. The basic diode structure was modified by adding nanostructured porous silicon (nanoPS) layers and by infiltrating silver nanoparticles (AgNPs) into the nanoPS layers, leading to Al/Si+nanoPS/TiO₂/NiCr and Al/Si+nanoPS+AgNPs/TiO₂/NiCr structures, respectively. The AC electrical properties were studied using a combination of electrochemical impedance spectroscopy and Mott–Schottky analysis, while the DC electrical properties were determined from current–voltage measurements. From the experimental results, an AC equivalent circuit model was proposed for the three different MIS Schottky barrier diodes under study. Additionally, the most significant electrical parameters were calculated. The results show a remarkable improvement in the performance of the MIS Schottky barrier diodes upon the addition of hybrid nanoPS layers with embedded Ag nanoparticles, opening the way to their use as photovoltaic devices.

Ti-doped ZnO thin films were obtained with the aim of tailoring ZnO film bioadhesiveness and making the optoelectronic properties of ZnO materials transferable to biological environments. The films were prepared on silicon substrates by sol–gel spin-coating and subsequent annealing. A Ti–O segregation limits the ZnO crystallite growth and creates a buffer out-layer. Consequently, the Ti-doped ZnO presents slightly increased resistivity, which remains in the order of 10^–3 Ω·cm. The strong biochemical interference of Zn²⁺ ions released from pure ZnO surfaces was evidenced by culturing Staphylococcus epidermidis with and without the Zn²⁺ coupling agent clioquinol. The Ti-doped ZnO surfaces showed a considerable increase of bacterial viability with respect to pure ZnO. Cell adhesion was assayed with human mesenchymal stem cells (hMSCs). Although hMSCs find difficulties to adhere to the pure ZnO surface, they progressively expand on the surface of ZnO when the Ti doping is increased. A preliminary microdevice has been built on the Si substrate with a ZnO film doped with 5% Ti. A one-dimensional micropattern with a zigzag structure shows the preference of hMSCs for adhesion on Ti-doped ZnO with respect to Si. The induced contrast of surface tension further induces a cell polarization effect on hMSCs. It is suggested that the presence of Ti–O covalent bonding on the doped surfaces provides a much more stable ground for bioadhesion. Such fouling behavior suggests an influence of Ti doping on film bioadhesiveness and sets the starting point for the selection of optimal materials for implantable optoelectronic devices.

As subwavelength nanostructures are receiving increasing attention for photonic and plasmonic applications, we grew nanostructured porous silicon (n-PS) and hybrid n-PS/Ag layers onto silicon substrates and measured their reflection and absorption characteristics as functions of the wavelength, angle of incidence, and polarization state of incident light. The experimental results show that the absorption characteristics of the hybrid n-PS/Ag layer can be controlled by selecting the appropriate combination of its thickness and porosity, together with the density of infiltrant silver nanoparticles. The observed wideband optical absorption characteristics of the hybrid n-PS/Ag layers might be useful in light-harvesting devices and photodetectors, since the overall efficiency will be increased as a result of increased field-of-view for both s- and p-polarization states of incident light.