The present invention relates to a device having a solid conjugated semiconductor comprising a hole transport material (HTM), wherein the hole transport material is mixed with oxidized hole transport material as a dopant; to a mixture which can be used as doped hole transport material; and to methods for the preparation of devices having a solid conjugated semiconductor. The present invention also relates to a solar cell comprising such a device and to other devices made with conjugated semiconductors, such as diodes (LEDs), transistors etc.