Falling squarely in the energy efficiency sector, Phononic, a developer of solid-state thermal management technology, just raised $44.5 million in in a Round D led by Eastwood Capital and the Wellcome Trust, along with WLR China Energy Infrastructure Fund, Tsing Capital, Venrock, Oak Investment Partners and Rex Health Ventures. The startup has raised more than $85 million in venture funding to date.

The 75-employee Phononic develops thermoelectrics -- materials that can convert a temperature gradient to a voltage or vice versa. The technology is a brilliant pursuit, but no one has brought it to mass markets economically or at scale just yet. Traditional thermoelectrics use materials such as bismuth telluride or silicon germanium, and more recently, silicon nanowires.

The near-term applications for Phononic's science are high-end refrigeration for labs and medical facilities, as well as cooling for fiber optics and data servers that are "necessary to continue Moore's law," according to the company. Phononic is looking to develop thermal management technology for consumer devices, and, more strikingly, to replace cheap, ubiquitous and century-old incumbent compressor technology.

CEO Anthony Atti told us this morning that the investment thesis around Phononic is that "semiconductors have revolutionized IT and LEDs, but have not had that same impact on cooling and heating." He notes that Phononic's thermoelectric technology is in the realm of Peltier cooling technology, but addresses three major shortcomings of that technology: efficiency, ability to scale, and ease of integration.

Atti said that Phononic is not just a device company; it will develop a system and go as far as developing a supply chain to support the new product. He suggested that when going against an entrenched incumbent, a startup can't just develop a component and then walk away. He added, "The extent to which we deliver a total solution is up to the market."

Atti claims that the compound semiconductor material used in his firm's thermoelectrics can be manufactured using high-volume, standard semiconductor tools and equipment.

Bruce Sohn, the former president of First Solar, is on the board at Phononic. When we spoke with him this morning, he told us that he had been working with the firm for four years and believes the startup is doing something "revolutionary that can do to compressors what the [integrated circuit] did to the vacuum tube."

Other companies developing thermoelectric technologies for cooling or capturing waste heat include the following: