Probing Photo-Physical Processes in Solid-state Organic Semiconductors Using Optical Pump - X-ray Probe Spectroscopy*

Fundamental understanding of photo-induced charge generation and charge transfer in organic semiconductors is of crucial importance for understanding the functionality of organic optoelectronics. Transient X-ray absorption spectroscopy (Tr-XAS) offers the opportunity for tracking photo-physical processes at the atomic and molecular scale. Here, using Tr-XAS combined with transient absorption spectroscopy and transient microwave conductivity, we investigate the local structure and time evolution of photoinduced charge-separated species in thin films of molecularly dispersed octabutoxy-Zinc(II) phthalocyanine (OButx-ZnPc) in a matrix of the well-known conjugated polymer poly(3-hexylthiophene) (P3HT). We probed a transient signal associated with OButx-ZnPc charged-species in the host polymer (P3HT). Our findings reveal that the XANES spectra of OButx-ZnPc and the transient signal are largely affected by the degree of order of the host material, which is tuned by the regioregularity of P3HT side chains (an amorphous regiorandom P3HT vs a semicrystalline regioregular P3HT.