Influence of Environmentally Affected Hole-Transport Layers on Spatial Homogeneity and Charge-Transport Dynamics of Organic Solar Cells.

After organic photovoltaic (OPV) cells achieved efficiency of more than 10%, the control of stability and degradation mechanisms of solar cells became a prominent task. The increase of device efficiency due to incorporation of a hole-transport layer (HTL) in bulk-heterojunction solar cells has been extensively reported. However, the most widely used HTL material, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), is frequently suspected to be the dominating source for device instability under environmental conditions.

Short-Term Environmental Effects and Their Influence on Spatial Homogeneity of Organic Solar Cell Functionality.

In this study, we focus on the induced degradation and spatial inhomogeneity of organic photovoltaic devices under different environmental conditions, uncoupled from the influence of any auxiliary hole-transport (HT) layer. During testing of the corresponding devices comprising the standard photoactive layer of poly(3-hexylthiophene) as donor, blended with phenyl-C-butyric acid methyl ester as acceptor, a comparison was made between the nonencapsulated devices upon exposure to argon in the dark, dry air in the dark, dry air with illumination, and humid air in the dark. The impact on the active layer's photophysics is discussed, along with the device physics in terms of integral solar cell performance and spatially resolved photocurrent distribution with point-to-point analysis of the diode characteristics to determine the origin of the observed integrated organic photovoltaic device behavior.

Interfacial Morphology and Effects on Device Performance of Organic Bilayer Heterojunction Solar Cells.

The effects of interface roughness between donor and acceptor in a bilayer heterojunction solar cell were investigated on a polymer-polymer system based on poly(3-hexylthiophene) (P3HT) and poly(dioctylfluorene-alt-benzothiadiazole) (F8BT). Both polymers are known to reorganize into semicrystalline structures when heated above their glass-transition temperature. Here, the bilayers were thermally annealed below glass transition of the bulk polymers (≈140 °C) at temperatures of 90, 100, and 110 °C for time periods from 2 min up to 250 min.

Enhanced nanoscale imaging of polymer blends by temperature-controlled selective dissolution.

Nanoscale imaging on polymer blends is vital, especially in organic electronics. By using temperature-controlled selective dissolution, the 3D structure of a thin film becomes accessible without the expensive search for adequate orthogonal solvents. The method, which takes advantage of the temperature dependence of the solubility, is demonstrated to image P3HT:PCBM and P3HT:F8TBT photovoltaic blend films using atomic force and scanning electron microscopy.