Solar Cells Info

Success in Trial Manufacture of BN/Si Heterodiode Solar Cell
September 04, 2008
Source: National Institute for Materials Science NIMS, Japan press release
http://www.nims.go.jp/eng/news/press/press080904-1.html
Abstract
1. A team led by Dr. Shojiro Komatsu, Group Leader of the Wide Band Gap Semiconductor Group, Advanced Electronic Materials Center of the National Institute for Materials Science (NIMS; President: Teruo Kishi) succeeded for the first time in the world in trial manufacturing a solar cell using high density boron nidtride (sp3-bonding BN), which is transparent to visible light and is one of the strongest of materials (high temperature refractory).
2. Active development of various energy saving technologies and new energy is underway in response to global warming and depletion/rising prices of fuel resources. Among these, popularization of solar cells by practical application of silicon solar cells is progressing worldwide. However, there is still a much room for the discovery and development of new solar cell materials with functions and features not found in silicon, and competition to develop these materials is intense. The BN/Si solar cell announced here was developed and successfully manufactured by NIMS before any other organization in the word. No other examples of this technology have been published to date.
3. BN has been considered a promising material, as it is a wide band gap1) semiconductor2) which enables production of ultraviolet (UV) lasers, transparent transistors, and other devices. However, the doping3) necessary to realize a semiconductor had been difficult with the conventional techniques. In this work, a BN/Si heterodiode4) was successfully produced for the first time in the world by using the original technique of laser mixing/plasma CVD in doping of a high density BN thin film. A prototype solar cell produced by this method displayed generating efficiency on the order of 2%. There is still a large gap between this and the level (18%) of today’s most advanced silicon solar cells. However, as data obtained with the world’s first prototype of a BN/Si heterodiode solar cell, it is considered a promising value for the future.
4. The laser mixing/plasma CVD method adopted here is a process in which doping of silicon progresses simultaneously with synthesis of high density BN (sp3-bonding BN), which has an interatomic bonding pattern similar to that in diamonds. It was possible to realize a BN/Si heterodiode for the first time using this technique. As a distinctive feature of the laser mixing/plasma CVD method, it is possible to produce solar cells in one step. Because the surface of the cell thin film is covered with micron-sized cones, which suppress reflection of sunlight, and light absorption efficiency of the film improves.
5. BN/Si solar cells will be commercialized in products designed for specialized applications, such as unmanned measuring devices, devises in space environment, etc. which have particularly severe requirements for durability, reliability, atmospheric corrosion resistance, and the like. In addition to the p-type BN which was successfully produced in this work, future plans include production of an n-type BN and a homodiode made entirely of BN. With BN homodiodes, cells which are transparent to visible light will be possible. This is expected to lead to the development of onboard sunroof power generating systems for automobiles, which can be used in combination with a storage battery, solar cells which can be applied to windows and sunglasses, and other devices.
6. This research achievement is scheduled for announcement at the 69th Autumn Meeting of the Japan Society of Applied Physics to be held at Chubu University on September 5, 2008.