The analysis of the efficiency of solar cells

Under the circumstances of the increasing depletion of fossil fuels, renewable energy, especially solar energy, is becoming more and more important. Thus, the methods of exploring solar energy are diverse and the energy conversion efficiency keeps rising while the cost keeps decreasing. Among all the methods, using solar cell is the main way to explore solar energy. Currently, solar cells can be divided into three main categories, crystalline silicon solar cells, thin film solar cells and novel solar cells. Crystalline silicon solar cells can also be divided into monocrystalline silicon solar cell and polycrystalline silicon solar cell. These two kinds of solar cells are the most common solar cells in our daily life. The efficiency of monocrystalline silicon solar cell is already pretty high reaching 25% while polycrystalline silicon solar cell reaches 21.3%. The stability of monocrystalline silicon solar is also better than that of polycrystalline silicon solar cell. The only fly in the ointment is that the cost of monocrystalline silicon solar is a little bit higher than polycrystalline silicon solar cell which makes monocrystalline silicon solar not optimal enough. Thin film solar cell includes amorphous silicon solar cells and multi-compounds solar cells. The transformation of solar cells from solid panel to thin film is one of the most significant breakthroughs of the second generation solar cell. The amorphous silicon solar cell becomes much cheaper than both monocrystalline silicon and polycrystalline silicon solar cells. But its drawback is obvious, its efficiency only reaches 13.6% which certainly needs to be improved. As for semiconductor compounds solar cells, there are made by various semiconductor materials. Major semiconductor compound solar cells contain chemical materials such as CdTe, CuInSe2(CIS), CuInSe2 doped Ga(CIGS), GaAs, InP, and multi-junction solar cell, etc. Materials like CdTe and CIGS can surely lower the cost of solar cells and their efficiencies are pretty high reaching 21.5% and 22.3%, respectively. But Cd is a toxic element while In and Se are rare elements, their reserves are limited. Materials like GaAs and InP are much more expensive comparing to others, but their efficiencies are pretty satisfying reaching 28.8% and 22.6%, respectively. More importantly, they have rather high radiation tolerance, especially InP solar cell has the best radiation tolerance among all kinds of solar cells. Thus, despite their high costs, they can still be used in many situations such as space station. As for multi-junction solar cell, the most prominent feature of it is the high efficiency. Solar cells with two junctions, three junctions and four junctions have reached the efficiencies of 31.6%, 37.9% and 38.8%. Obviously, multi-junction solar cells are the best choice to improve energy conversion efficiency. The novel solar cell consists of organic solar cells, dye-sensitized solar cells, quantum dot solar cells and hybrid perovskite solar cells. Among all these third generation solar cells, perovskite solar cell is the most promising one due to its superior properties and rapid improvement. Its efficiency has already reached 21% in only a few years. But more work needs to be done to improve its properties such as its stability and currently perovskite solar cell still contains lead which is toxic and may need to be replaced. This paper starts from analyzing the theoretical efficiency of solar cells, then compares those theoretical efficiencies with experimental efficiencies to present the expectation of different kinds of solar cells.