- Amorphous Silicon (a-Si) Photovoltaic
- Hydrogenated amorphous silicon (a-Si:H, abbreviated to a-Si) is the most well-developed thin film photovoltaic (PV) technology. Atoms of a-Si form a continuous random network without crystalline structure over large range and dangling bonds exists due to this disorder nature. Hydrogen passivation significantly reduces the defect density of dangling bond and leads to superior electro-optical properties. The selection rules that weaken absorption in crystalline silicon (abbreviated to c-Si) do not apply to a-Si because it is amorphous. Therefore its light absorption capability is 500 times greater than c-Si. Only very thin a-Si layers in p-i-n sequence are required as active layer (~300 nm).
- a-Si/μc-Si Tandem Photovoltaic
Light-induced degradation is a well-known issue for a-Si PV, which suffer from the Staebler-Wronski effect. The power output of a-Si PV degrades to a certain level after a period of sunlight exposure and then keeps stablized. However, the Staebler-Wronski effect is not shown on hydrogenated microcrystalline silicon (μc-Si:H, abbreviated to μc-Si) PV which is composed of an amorphous phase and of nanocrystalline grains. In addition, the wavelength of spectrum absorbed by μc-Si (infrared) is longer than that of a-Si (visible light) and results in more utilization of sunlight radiance. The double junction tandem structure formed by stacking a μc-Si bottom cell (Eg = 1.2 eV) onto an a-Si top cell (Eg = 1.7 eV) in a series connection gains higher energy conversion efficiency than a-Si single junction alone. The power output of a-Si/μc-Si tandem PV increases significantly. For a-Si/μc-Si tandem PV, several micrometers thick μc-Si layer is required to achieve current-matching with a-Si while advanced light enhancement schemes need to be used.
- Silicon Thin Film Photovoltaic Processes
- The manufacturing process is to deposited active layer of silicon thin film by PECVD (Plasma Enhanced Chemical Vapor Deposition) onto a TCO (Transparent Conductive Oxide) coated glass, following the sputtering of the back electrode, which consists of a TCO layer and a high reflective metal layer. After that, silicon thin film PV modules are completed by ribbon soldering, EVA/back sheet lamination and then the final framing assembly.