Next Generation

Light farm


By Lydialyle Gibson
Image courtesy Argonne National Laboratory

To make solar cells a more economically feasible alternative to oil and gas—material and manufacturing costs currently make them prohibitive—scientists at Chicago and Argonne National Laboratory have been reinventing the design. In a study published in the August 3 Small, U of C chemist Steven Sibener, chemistry postdoc Sanja Tepavcevic, and Argonne researchers Seth Darling, PhD’02, and Nada Dimitrijevic described a technique for manufacturing solar cells by creating tubes of semiconducting material and then growing polymers directly inside them. 

Today most solar cells are made from crystalline silicon or cadmium telluride, and growing high-purity crystals requires tremendous energy and labor. Hybrid solar cells are the next generation, blending cheaper organic and inorganic materials. The Chicago team does this by growing organic polymers inside inorganic nanotubes.

At its most basic level, solar-cell technology relies on a process that begins when particles of light strike a semiconductor, whose power to transmit electricity is intense at high temperatures and nearly nonexistent at low ones. When a photon hits the cell, it excites one electron out of its initial state, leaving behind a hole of positive charge. Hybrid solar cells contain two types of semiconducting material: one conducts electrons, the other holes. At the junction between the two, the electron-hole pair gets pulled apart, creating a current.

Initially, the researchers planned to take titanium dioxide, a semiconductor that sprouts nanotubes (above) 10,000 times smaller than a human hair, and fill those tubes with an organic polymer. But the task proved frustrating; Darling described it as “trying to stuff wet spaghetti into a table full of tiny holes.” So the team re-engineered the process, filling the tubes instead with a “polymer precursor” and then turning on an ultraviolet light. The polymer grew inside the tubes. Later testing showed that the two materials can capture light at wavelengths that neither could alone.

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