Charge-transporting thin-films which contain a charge-transporting oligomer or polymer are commonly used as the charge injection layer, charge transport layer or emissive layer in organic electroluminescence devices (abbreviated below as “organic EL devices”).
These charge-transporting thin-films are required to have a high flatness. This is because surface irregularity of the charge-transporting thin-film leads to, for example, uneven light emission by the device, a shortened device life, dark spot formation, and lowering of the device characteristics due to electrical shorting, and is thought to bring about a decline in yield during the production of organic EL devices.
Accordingly, there exists a strong desire for a technology that is industrially feasible and is capable of forming charge-transporting thin-films of high flatness.
Charge-transporting thin-film forming processes are broadly divided into dry processes such as vacuum deposition and wet processes such as spin coating.
Comparing dry processes and wet processes, the latter processes are capable of easily producing thin-films having a high flatness and thus can be expected to improve the device yield.
For reasons such as this, it is wet processes that are predominantly used in the industrial fabrication of organic EL devices.
In light of the above, the inventors have developed charge-transporting varnishes for producing, by wet processes, charge-transporting thin-films applicable to various types of electronic devices (see, for example, Patent Documents 1 to 3).
However, given the advances being made in the area of electronic displays, such as the trend in recent years toward larger devices for displaying graphics, there has been a growing need for charge-transporting varnishes which are capable of very precise and reproducible film formation over a large surface area. Existing varnishes have not always been able to fully satisfy such a need.