Spectroscopy of organic semiconductor devices

Abstract

Optoelectronic devices based on conjugated organic materials are becoming an attractive alternative to their inorganic counterparts due to their low cost and increased versatility, since they combine semiconducting properties with the processability and chemical diversity of polymers and small molecules. Organic solar cells, photodetectors and light-emitting diodes are examples of such devices. However, improvements in their performances and device life-time depend on a deep knowledge about the photophysical and electronic processes that occur in the materials. In this proposal we aim at investigating the dynamics of charge recombination and extraction in organic solar cells, by combining transient photoinduced absorption (PA) spectroscopy and transient photocurrent (PC) measurements. During the candidate's stay at IFSC-USP, he will get acquainted with the PA and PC setups, help in extending our current continuous wave-PA setup to perform transient PA with ns to ms temporal resolution, and use it to investigate charge recombination dynamics in organic solar cells. He will also get acquainted with nonlinear spectroscopy methods based on second-harmonic generation (SHG) and sum-frequency generation (SFG) that we are currently using to probe electric fields in organic devices, with the main goal of probing the field distribution in organic field-effect transistors (OFETs). The candidate has extensive experience in fabrication and characterization of organic solar cells. He was active in the research towards understanding the role of donor-acceptor interface in a heterojunction solar cell, i.e., Organic-Inorganic interface for dye sensitized solar cells (DSSC) and Hybrid cells, Organic-Organic interface for polymer solar cells, Organic-Organic-Inorganic double interface for solid-state DSSC. He had worked extensively on femtosecond transient spectroscopy absorption (fs-TAS) of donor systems (D-p-A molecules, semiconducting polymers, energy relay dyes) and their interface with metal oxides acceptors like anatase TiO2, ZnO, SnO2. Recently, he has developed working knowledge in nanosecond-millisecond time-resolved spectroscopy, Photocurrent spectroscopy and THz spectroscopy. The exchange of experiences during this stay may be the starting point of a long-term collaboration between the two groups at IFSC-USP and IIT Hyderabad. (AU)