Influence of hole extraction efficiency on the performance and stability of organic solar Cells

We demonstrate the impact of the hole extraction efficiency on the device performance and stability of organic solar cells. We present results on organic solar cells prepared with a poly(aniline) (PANI) based hole transport layer (HTL) blended with varying concentrations of poly(styrene sulfonate) (PSS), leading to differences in the HTL transmittance and conductivity. The PANI to PSS ratios investigated here were 1:1, 1:2 and 1:5. The initial power conversion efficiency of the devices is demonstrated to depend directly on the HTL conductivity, showing increasing performance with decreasing PSS content. However, after degradation of encapsulated solar cells under illumination, it is observed that the higher PSS content results in better stability. Data from impedance spectroscopy offers detailed insight into the interface properties, and detailed equivalent circuit analysis allows us to correlate the decreased hole extraction capabilities to the HTL properties and to the power conversion efficiency of the solar cell.