What if solar electricity was cheaper than fossil fuel power? How would that drive our economy and stabilize geo-political tensions? How would the climate change for the better? How would access to basic lighting help to reduce poverty on a global scale?
I am proposing a new concept that can lead to solar panels with greater than 20% efficiency and costs less than $0.50/Watt leading to electricity costs of less than $0.06/kWh.
Existing thin-film photovoltaic (TFPV) technologies are commercially available (about 10% of global market share) and have the distinct advantages of high-throughput deposition methods and material flexibility. Although TFPV laboratory devices based on various materials have recently achieved greater than 20% efficiency, further advancements are required to tighten the gap between small cell and large panel performance (now less than 15% efficient), reduce cost, and improve long-term reliability (TFPV adoption suffers from degradation).
Conventional TFPV cells are comprised of several stacked layers of semiconductors and dielectrics sandwiched between electrodes, with a transparent conducting oxide (TCO) acting as the electrode on the illuminated side. Other layers are required to form pn-junctions and passivation regions which improve performance. However, with each layer comes interfaces which always carry with them high densities of recombination centers, energy barriers, and seeds of degradation. Furthermore, making the panels requires scribing out contact lines which causes damage and shadow losses.
As an alternative to the conventional stacked approach, I have developed the concept of an All-Back-Schottky-Contact (ABSC) TFPV device architecture wherein two dissimilar metals of different work functions are adhered to the non-illuminated side of the device. Reach-through Schottky junctions and the difference in work functions of the two metals establish the built-in field. The basic philosophy of this design paradigm is to minimize the number of interfaces through which charge transport is required. A schematic layout is shown in Fig. 1.
Some of the main advantages of the ABSC design include:
• No front contact lines, TCO, pn-junctions, or window layers, thus reducing parasitic photon absorption and interface issues.
• No scribing requirements for module fabrication, reducing damage and shadow losses.
• Design optimization via optical control and back contact shape/size.
• Fewer interfaces which are prone to degradation.
• Reduced losses in going from cell to panel.
My simulations using COMSOL Multiphysics® have shown that a practically simple design can achieve greater than 20% light to electricity conversion efficiency (see Fig. 2). Removing the extra manufacturing steps can also drastically reduce costs.
In this work, COMSOL was employed to transform fundamental physical concepts and practical experience into a viable design concept that can be realized with established fabrication techniques. The fabrication techniques include photolithography, which has been perfected in the semiconductor industry, and material deposition methods that are standard in the thin-film photovoltaics industry. Working with my colleagues at the DOE National Renewable Energy Lab we are well-positioned to fabricate and characterize the proof of concept device.
With this design, we can make solar electricity cheaper than coal and create a better future.