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/Oxidethin 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 (Voc) and current density (Isc). 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 Voc as high as −0.74 V and Isc 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.