Direct Patterning of Conductive Polymer Domains for Photovoltaic Devices

We report a simple approach to control the morphology of polymer/fullerene solar cells based on electron-beam patterning of polymer semiconductors. This process generates conductive nanostructures or microstructures through an in situ cross-linking reaction, where the size, shape, and density of polymer domains are all tunable parameters. Cross-linked polymer structures are resistant to heat and solvents, so they can be incorporated into devices that require thermal annealing or solution-based processing. We demonstrate this method by building “gradient” and nanostructured poly­(3-hexylthiophene)/fullerene solar cells. The power-conversion efficiency of these model devices improves with increasing interfacial area. The flexible methodology can be used to study the effects of active layer design on optoelectronic function

A plot of the optimized squareness value, <i>n</i>, vs etch time.

<p>A plot of the optimized squareness value, <i>n</i>, vs etch time.</p

SEM image of a 75nm wide square pattern fabricated by SLIM processing of a dot array with 100nm pitch.

<p>SEM image of a 75nm wide square pattern fabricated by SLIM processing of a dot array with 100nm pitch.</p

A plot of pattern size vs etch time for different precursor openings showing little change in the pattern size distribution.

<p>A plot of pattern size vs etch time for different precursor openings showing little change in the pattern size distribution.</p

Nickel was electrodeposited into a SLIM pattern with 80nm square opening.

<p>The SEM images show a) a 52 degree projection of the nickel pillars after removing the resist and (b) a 52 degree projection of the same sample after argon plasma treatment.</p

A plot showing the influence of SLIM process time and precursor thickness on the pattern width.

<p>Each curve approaches an asymptote at approximately 183nm revealing the self-limiting etch process.</p

The SEM images compares a) a SLIM processed pattern and b) the same sample after heat treatment for one hour at 400 °C.

<p>The SEM images compares a) a SLIM processed pattern and b) the same sample after heat treatment for one hour at 400 °C.</p

SEM image of preferred orientation of 400 nm thick rod-shaped magnetic particles.

<p>The particles were fabricated using horizontal movement of the AAL stage and evaporation of gold/permalloy/gold tri-layers. The sample was lifted-off in TMAH solution, rinsed in DI water to remove the traces of TMAH and dried on a silicon surface in the absence of any external magnetic field. The observed preferred orientation of the particles is the result of shape anisotropy dominating the material properties. The rods’ alignment into the long-stranded pattern is the manifestation of the switching of easy axis along the length of the particles due to their shape.</p

Diagram describing the SLIM process.

<p>The precursor is dot patterns separated by a wall of thickness a₀ and b₀. SLIM processing narrows both walls at the same rate to a thickness of a₁ and b₁. At a critical thickness the etch rate reduces significantly resulting in little change towards a₂, but b₂ continues to narrow. As b₂ approaches the critical thickness, the pattern converges to a square.</p

Summary of coercivity and remnant magnetization of magnetic particles with permalloy layers 40–300 nm thick.

<p>Summary of coercivity and remnant magnetization of magnetic particles with permalloy layers 40–300 nm thick.</p