Hybrid solar cells based on MEH-PPV and thin film semiconductor oxides (TiO2, Nb2O5, ZnO, CeO2 and CeO2–TiO2): Performance improvement during long-time irradiation

Performance improvement of hybrid solar cells (HSC) applying five different thin film semiconductor oxides has been observed during long-time irradiation in ambient atmosphere. This behavior shows a direct relation between HSC and oxygen content from the environment. Photovoltaic devices were prepared as bi-layers of thin film semiconducting oxides (TiO₂, Nb₂O₅, ZnO, CeO₂–TiO₂ and CeO₂) and the polymer MEH-PPV, with a final device configuration of ITO/Oxide_{thin film}/MEH-PPV/Ag. The oxides were prepared as thin transparent films from sol–gel solutions. The photovoltaic cells were studied in ambient atmosphere by recording the initial values of open circuit voltage (V_oc) and current density (I_sc). Solar decay curves presented as the measurement of the short circuit current as a function of time, IV curves and photophysical analyses were also carried out for each type of device. Solar cells with TiO₂ thin films showed the best performance with maximum V_oc as high as −0.74 V and I_sc of 0.4 mA/cm². Solar decay analyses showed that the devices require a stabilization period of several hours in order to reach maximum performance. In the case of TiO₂, Nb₂O₅ and CeO₂–TiO₂, the maximum current density was observed after 15 h; for CeO₂, the maximum performance was observed after 30 h. The only exception was observed with devices applying ZnO in which the current density decreased drastically and degraded the polymer in just a couple of hours.