Conclusions and outlook

Although conventional SCs based on inorganic materials specially Si exhibit high efficiency, very expensive materials and energy intensive processing techniques are required. In comparison with the conventional scheme, the hybrid Si-based SC system has advantages such as; (1) Higher charging current and longer timescale, which make the hybrid system have improved performances and be able to full-charge a storage battery with larger capacity during a daytime so as to power the load for a longer time; (2) much more cost effective, which makes the cost for the hybrid PV system reduced by at least 15% (Wu et al.,

2005) . Therefore, hybrid SCs can be suitable alternative for conventional SCs. Among hybrid SCs which can be divided into two main groups including HJ hybrid SCs and dye-sensitized hybrid SCs, HJ hybrid SCs based on Si demonstrate the highest efficiency. Thus, the combination of a-Si/pc-Si has been investigated. These configurations of SCs can compensate the imperfection of each other. For example, a-Si has a photo-degradation while a pc-Si cell is stable so the combination is well stabilized. Furthermore, applying textured structures for front and back contacts and implementing an IRL between the individual cells of the tandem will be beneficial to enhancement of the efficiencies in these types of hybrid SCs. Due to recent studies; a-Si/pc-Si (thin film cell) has an efficiency of about 11.9%. Another study is done over three stacked cell of a-Si:H/pc-Si/c-Si (triple), which will be less sensitive to degradation by using the thinner a-Si. The last efficiency reported for a-Si/a – SiGe/a-SiGe (tandem) is about 10.4% and for a-Si/nc-Si/nc-Si (tandem) is approximately 12.5%.

Furthermore, Si based SC systems are being characterized to low temperature coefficient, the design flexibility with a variety of voltage and cost potential, so it can be utilized in large scale. In near future, it will be feasible to see roofs of many private houses constructed by thin film Si solar tiles. Although hybrid SCs are suitable replacements for conventional SCs, these kinds of SCs based on inorganic semiconductor nanoparticles are dependent on the synthesis routes and the reproducibility of such nanoparticle synthesis routes. The surfactant which prevents the particles from further growth is, on the other hand, an insulating layer which blocks the electrical transport between nanoparticles for hybrid SCs son such surfactants should be tailored considering the device requirements. Therefore, there is an increased demand for more studies in the field of hybrid SCs to find solutions to overcome these weak points.

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