Debra Mascaro

spin-enhanced organic bulk heterojunction photovoltaic solar cells

Recently, much effort has been devoted to improve the efficiency of organic photovoltaic solar cells based on blends of donors and acceptors molecules in bulk heterojunction architecture. One of the major losses in organic photovoltaic devices has been recombination of polaron pairs at the donor-acceptor domain interfaces. Here, we present a novel method to suppress polaron pair recombination at the donor-acceptor domain interfaces and thus improve the organic photovoltaic solar cell efficiency, by doping the device active layer with spin 1/2 radical galvinoxyl. At an optimal doping level of 3 wt%, the efficiency of a standard poly(3-hexylthiophene)/1-(3-(methoxycarbonyl)propyl)-1-1-phenyl)(6,6)C(61) solar cell improves by 18%. A spin-flip mechanism is proposed and supported by magneto-photocurrent measurements, as well as by density functional theory calculations in which polaron pair recombination rate is suppressed by resonant exchange interaction between the spin 1/2 radicals and charged acceptors, which convert the polaron pair spin state from singlet to triplet.

Stretchable fingernail sensors for measurement of fingertip force

This paper describes a novel stretchable fingernail sensor for measuring fingertip forces for human-computer interaction. The fingernail sensor uses photoplethysmography to measure the change in blood perfusion in the fingernail bed when the fingerpad touches a surface with various forces. The original fingernail sensor was rigidly attached to the human fingernail, necessitating a customized fabrication for each individual user. Using novel fabrication techniques, a new stretchable sensor has been developed, where optoelectronic components are embedded within a soft rubber substrate, connected by stretchable conductors. This stretchable sensor can conform to the two-dimensional curvature of any human finger, eliminating the need for individual customization. In this paper, we demonstrate the successful fabrication of a prototype sensor with two LEDs and two photodetectors