Physics and Technology of Carrier Selective Contact Based Heterojunction Silicon Solar Cells

AbstractThis chapter redefines silicon-based solar cells by introducing the concept of charge-carrier selective contacts. In this sense, heterojunction solar cells use crystalline silicon as a high-quality light absorber. Then, two complementary electron- and hole-transport-layers must select the photogenerated charge-carriers at their corresponding electrodes. The solar cell electrical characteristics can be explained considering the electrochemical-potential as the driving-force for electrons flow. It is shown that doped p–n junctions are not essential for effective photovoltaic energy conversion, though they are indeed a good and very mature solution. Alternatively, non-conventional materials can be used as selective contacts for silicon heterojunction solar cells with important technological advantages. Transition-metal-oxides have particularly excelled as the hole-selective-contacts of silicon heterojunction solar cells. Regarding the electron-selective-contact, titanium oxide is probably the most studied alternative. Full dopant-free silicon heterojunction solar cells with efficiencies above 20% have been already demonstrated. These devices can be fabricated at low-temperature by simple deposition techniques and using safe and abundant materials. On the other hand, the metallic electrode is also very important to design good charge-carrier selective contacts. It is shown that dipolar interface layers can apparently shift the work function of the electrode and reinforce its charge-carrier selectivity. The most novel approaches based on the use of spin-coated conjugated polyelectrolytes is explained by the end of this chapter.KeywordsCarrier-selective contactElectron-transport-layerHole-transport-layerDopant-freeSilicon heterojunctionTransition-metal-oxideInterface dipole