Materials for cheap solar cells can handle oxygen for the first time
Ashley Marshall

New protective atoms on the surface of quantum dots have led to the assembly of the first, air-stable lead selenide (PbSe) quantum dot (QD) solar cell. Researchers show record efficiencies for this material with the added benefit of being made in air as opposed to a nitrogen-filled box. Reproduced with permission. Copyright 2014: American Chemical Society.

Solar cells have been showing up everywhere you look, from commercial buildings, to residential neighborhoods, to huge solar farms just outside of cities. Solar panels are often prohibitively expensive, partly because of their high manufacturing costs. Researchers at the Center for Advanced Solar Photophysics (CASP) are exploring a new class of materials that would allow solar cells to be manufactured from solution, like printing ink onto paper or painting a wall. This manufacturing process allows quicker and cheaper production of solar cells.

These materials are known as quantum dots (QDs), which are extremely small particles—so small that 20,000 particles lined up would just span the width of a human hair. Materials this small interact with light differently than a large piece of the same composition. At CASP, scientists work to improve the process of making these QDs and apply the new interactions with light to improve current solar cell technology.

One of the greatest challenges in using QDs is that certain types suffer greatly from degradation when exposed to oxygen. Many of the solar cells made from these small particles require completely air-free conditions during fabrication. Researchers at CASP developed a groundbreaking synthesis that includes protective agents for lead sulfide (PbS) and lead selenide (PbSe) QDs, shielding the materials from oxygen by protecting the surface. This new synthesis includes the protecting atoms as a part of the initial ingredients so that no extra steps or chemicals are required to make the air-stable version of the QDs. This lowers the overall cost and time of the material synthesis.

Using these protected QDs, the team fabricated the first-ever air-stable PbSe devices with the best devices converting 6.2 percent of sunlight into electricity, the highest reported efficiency. As an added benefit, the devices show good air stability even after being exposed to oxygen for multiple days.

Researchers also showed that the new synthesis can be scaled up—paving the way for large-scale industrialization of this material. While previous synthetic methods yielded ~1 gram of material (about the same weight as two Tic Tac® mints), CASP researchers successfully produced 47 grams of PbS in a single batch, without the use of inordinately harmful chemicals. Further advancements will lower the barrier to commercialization and bring the future of renewable energy closer.

More Information

Zhang J, J Gao, EM Miller, JM Luther, and MC Beard. 2014. "Diffusion-Controlled Synthesis of PbS and PbSe Quantum Dots with in Situ Halide Passivation for Quantum Dot Solar Cells." ACS Nano 8(1):614-622. DOI: 10.1021/nn405236k

Zhang J, J Gao, CP Church, EM Miller, JM Luther, VI Klimov, and MC Beard. 2014. "PbSe Quantum Dot Solar Cells with More than 6% Efficiency Fabricated in Ambient Atmosphere." Nano Letters 14(10):6010-6015. DOI: 10.1021/nl503085v


This material is based upon work supported by the Center for Advanced Solar Photophysics, an Energy Frontier Research Center, funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences. DOE funding was provided to NREL through contract DE-AC36-08G028308. In the Nano Letters article, the X-ray photoelectron spectroscopy work was conducted with support from a National Renewable Energy Laboratory (NREL) Director’s Postdoctoral Fellowship. In the ACS Nano article, EMM was supported with an NREL Director’s Postdoctoral Fellowship award.

About the author(s):

Ashley Marshall is a graduate student in the Center for Advanced Solar Photophysics (CASP), working at the National Renewable Energy Laboratory through the University of Colorado, Boulder. Her research focuses on using quantum dots in solar cells to utilize unique photophysics, which will allow us to overcome the theoretical efficiency limits in solar cells.

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