Semiconductor Polymer/Top Electrode Interface Generated by Two Deposition Methods and Its Influence on Organic Solar Cell Performance.

In this Research Article, the effect of two techniques for top-electrode deposition in organic photovoltaics (OPVs) cells with the configuration ITO/PEDOT:PSS/PTB7-Th:PCBM/PFN/top-electrode is analyzed. One deposition was made by evaporation under high vacuum, meanwhile the other was carried out at normal room atmosphere; for the former, a double layer of Ca and the eutectic alloy Field's metal (FM) was thermally evaporated, while for the latter FM was deposited just by melting and dropping it on top of the delimited active area at temperatures about 90 °C. The average short-circuit photocurrent density, open circuit voltage and fill factor for devices with either Ca/FM (evaporated) or FM (by dripping) cathode, were very similar: around 13.20 mA/cm, 840 mV, and 0.6, respectively. Average efficiency for devices with the mentioned evaporated cathode was of 6.4% (largest value 7.0%), meanwhile for devices with the cathode deposited by dripping, it was of 6.1% (largest value 6.5%). Morphological analysis, by atomic force microscopy on the surface of a FM electrode, detached from an OPV device, shows inhomogeneities and pinholes in its surface with an average roughness of 16 nm. OPV photocurrent was studied by means of laser beam induced current (LBIC), it showed that OPVs devices with FM top electrode exhibits an inhomogeneous response. An impedance analysis was also carried out and results were correlated with defects observed at the studied interface. In spite of the mentioned deficiencies at FM interface, overall PV performance of devices with this electrode highlights the convenience of using FM because of its easy, fast, and low-cost deposition (vacuum free) characteristics.