Fabrication techniques solution processing

Fabrication of solution-processed multilayered organic light-emitting diodes (OLEDs) from oxetane-ftinctionalized precursors, which are commonly photochemically cross-linked by UV radiation in the presence of a photoinitiator, has been reported recently. The reaction proceeds via CROP. Insoluble cross-linked polymer networks were obtained using precursors that contain two or more oxetane units per molecule. This novel approach simplifies OLED fabrication, and is generally compatible with various deposition/printing techniques. 

The utilization of solution-processable techniques for the fabrication of Pc-based nanoscale systems represents a relatively cheap and technologically appealing methodology, when compared to vacuum techniques, for the preparation of nano-structured architectures. 

Anisotropic etching of silicon is routinely used in the fabrication of three-dimensional structures [1,2]. These micro fabrication techniques take advantage of orientation-dependent etch rates where the planes of lowest etch rate, usually the (111) planes, act as etch stops for the dissolution process [3, 4]. In electrolytes such as KOH, the etch rates of the (100) and the (110) planes may be more than two orders of magnitude faster than those of the (111) planes. In buffered NH4F solutions, etch rate enhancements as high as 15 have been reported for the (100) plane in comparison with the (111) surface [5]. 

In addition to vacuum-deposited small-molecule structures, bilayer devices have been fabricated from conjugated polymers and other solution-processible materials. One study reports a 1.9% efficient device fabricated by lamination of two spin-coated polymer layers (Granstrom et al, 1998). In principle, polymer bilayers can also be fabricated by spin-coating of successive layers using incompatible solvents. A more practical route to planar bilayers is the deposition of successive layers that have previously been spin-coated and removed from the substrate by a float-off technique (Ramsdale et al, 2002). 

To reduce the cost of solar cells, it is desirable to start with raw materials that are cheaper, easier to process, and amenable to low-cost deposition techniques. In particular, it is desirable to use materials that can be deposited from solution or from the vapor phase onto a flexible substrate. This would permit the use of high-throughput fabrication techniques such as reel-to-reel processing and web coating, enabling more rapid production that would greatly lower costs. Molecular semiconductors are one class of materials that meet these processing requirements. 

Due to its high melting point, P30 cannot be processed by injection molding or extrusion teehniques. However, P30 ean be fabricated by solution casting techniques into films or by wet spin techniques into fibers. On orientation or heat treatment, these materials beeome insoluble. 

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