Organic photovoltaic (OPV) solar cells are inexpensive to produce but suffer from low efficiencies, which ultimately prevent their widespread use. Some success has been achieved using polymer based active layers, which absorb strongly in the blue-green region of the solar spectrum. However, a power conversion efficiency (PCE) of 10% must be achieved for commercial viability and incorporation of a near infra-red (NIR) low-band-gap-absorbing dye is necessary to accomplish this goal. Many groups have therefore explored NIR sensitizer addition to their OPVs but many promising low band-gap materials have shown poor PCE or difficulties in processing. A substantial need remains for new materials and new developments in fabrication of NIR-active OPVs.
This project investigates novel, solution processable squaraine dyes, targeted specifically for optimal application in NIR bulk heterojunction active layers for tandem OPVs. The work is designed based on a systematic variation of the functional groups on synthesized squaraines and a measure of the associated impact on isolated variables such as solubility, solid state morphology and aggregation, molecular orbital energy levels, interaction strength with fullerene electron acceptors, and excited state lifetime. Functional group substitution will be exploited because of the large number of potential synthetic precursors. Thus, an appropriate solubility and film morphology will be dialed in, beneficial since conductive properties are associated with the order and packing of the molecules in the solid state. Resulting optical absorbance red-shifts and energy level changes will also be explored. The long term goal is to describe how squaraine dyes must be chemically modified to achieve high PCEs for commercial viability. In application-driven research, an empirical approach is commonly used to meet goals for better device performance. However, a strong complementary approach is involved in this work on the prescription for how devices can be improved by fully understanding all contributing variables and mechanisms for efficient operation. To achieve the highest PCEs an interdisciplinary approach will be utilized making use of the team?s ability to i) make, measure and optimize devices, ii) test a complete range of individual properties contributing to device efficiency and iii) synthesize new compounds.
The results from this project will help enable more efficient, affordable and sustainable solar cells. Participating students will develop a fundamental confidence and understanding in chemistry, materials science and device engineering that can be universally applied. Research experiences and publication opportunities for graduates and, importantly, a large number of undergraduates will be provided.
