Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 119, Issue 19, Pages 10304-10313Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.5b02971
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Funding
- Center for Interface Science: Solar Electric Materials (CISSEM)
- U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0001084]
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The effect of the molecular orientation distribution of the first monolayer of donor, molecules at the hole harvesting contact in an organic photovoltaic (OPV) on device efficiency-was investigated. Two zinc phthalocyanine(ZnPc) phosphonic acids (PA) deposited on indium tin oxide (ITO) electrodes are compared: ZnPC(PA)(4) contains PA linkers in all four quadrants, and ZnPcPA contains a PA linker in one quadrant. ZnPcPA. monolayers exhibited a broad distribution of molecular orientations Whereas ZnPc(PA)(4) adsorption produced a monolayer with a narrower orientation distribution with the molecular plane more parallel to the ITO surface, We used potential-modulated attenuated total reflectance spectroelectrochemistry (PM-ATR) to characterize the charge-transfer kinetics of these films and show that the highest rate constants correspond: to ZnPc subpopulations that are oriented more parallel to the ITO surface plane. For ZnPc(PA)(4), rate constants exceeded 10(4) s(-1) and are among the highest ever reported for a surfaceconfined, redox couple, which is attributable to both its Orientation and the small ZnPc-electrode separation distance. The performance of OPVs with ITO hole-harvesting contacts modified with ZnPc(PA)(4) was comparable to that achieved with highly activated bare ITO contacts, whereas for ZnPcPA-modified contacts, the OPV performance was similar to that-observed with (hole-blocking) alkyl-PA modifiers. These results demonstrate the synergism between molecular structure, energetics, and dynamics at interfaces in OPVs.
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