A University of Minnesota research team has 3D-printed an array of light receptors on a hemispherical surface, in a first step toward creating a “bionic eye” that could someday help blind people see or sighted people see better. Using their custom-built 3D printer, the researchers started with a base ink of silver particles. The ink, when dispensed on the surface of a hemispherical glass dome, stayed in place and dried uniformly instead of running down the curved surface. The researchers then used semiconducting polymer materials to 3D-print photodiodes, which convert light into electricity. The high-performance polymer-based photodetectors were characterized, and the devices were integrated into image sensing arrays with high sensitivity and wide field of view. Researchers at the University of Minnesota have fully 3D-printed an image sensing array on a hemisphere, which is a first-of-its-kind prototype for a “bionic eye.” Courtesy of University of Minnesota, McAlpine Group. Professor Michael McAlpine, leader of the research team, said the most surprising part of the process was the 25 percent efficiency — a level comparable to that of microfabricated counterparts — that the team achieved when converting the light into electricity with the fully 3D-printed semiconductors. “We have a long way to go to routinely print active electronics reliably, but our 3D-printed semiconductors are now starting to show that they could potentially rival the efficiency of semiconducting devices fabricated in microfabrication facilities,” McAlpine said. “Plus, we can easily print a semiconducting device on a curved surface, and they can’t.” The 3D-printed optoelectronic devices could allow for flexibility in the design and manufacturing of next-generation wearable and 3D-structured optoelectronics — in addition to validating the potential of 3D printing to achieve high-performance, integrated, active electronic materials and devices. McAlpine said the next steps would be be to create a bionic eye prototype with more light receptors and even greater efficiency. The team would also like to investigate printing on a soft hemispherical material that could be implanted into a real eye. The research was published in Advanced Materials (doi: 10.1002/adma.201803980). This video shows the 3D-printing process for directly and fully 3D-printing an array of interconnected semiconducting photodiode (light receptor) devices on a glass hemisphere. Courtesy of University of Minnesota, McAlpine Group.