Riyadh College of Technology

In this paper, we demonstrated that aluminum films deposited on the front surface of multi-crystalline silicon (mc-Si) provide excellent surface passivation and high electronic quality of such materials.A thickness of about 8 μm of aluminum films was deposited by a screen-printed on the front surface of the mc-Si annealed for 20 min at 500 °C.The immersion of multi-crystalline silicon in HF/H₂O₂/HNO₃ after the film deposition is the key factor in achieving the high electronic quality front surface of mc-Si nanostructures (mc-Si-NS).As a result, the total reflectivity drops to about 2% and a low surface recombination velocity of about 1.5 cm s^-1 was obtained.These results indicate that multi-crystalline silicon surface passivation using the aluminum layer is a valuable process to improve the efficiency of the mc-Si-NS based solar cells.

In multi-crystalline silicon (mc-Si), the detrimental effect of impurities and grain boundaries (GBs) on charge carrier transport has driven the research focus since many years.In view of curing these limitations, we present an innovative method to enhance the optoelectronic performance of mc-Si wafers via a combination between GBs grooving and porous silicon (PS) gettering.A preferential grooving of GBs was achieved using the HF/HNO₃ based solution, the PS layers were formed on both sides of the samples using stain-etching method and the gettering experiment was performed at temperatures ranging from 750 to 900 °C.As a result, it has been shown that the rapid thermal annealing process with chem. grooving gives a pos. trend of improvement of the electronic quality and found to be more efficient when used in combination with PS.After removing the PS layer, the minority carrier lifetime increases by a factor of more than 27.In addition, a significant enhancement of majority carrier mobility was obtained, which led to an important decrease of the resistivity.

Metal nanoparticle assisted chem. etching (MNpACE) is developed wet etching method for producing uniform semiconductor nanostructure (silicon nanowires) from patterned metallic film on crystalline silicon surface.The metal films facilitate the etching in HF and H₂O₂ solution and produce silicon nanowires (SiNWs).The creation of different SiNWs morphologies by changing the etching time and its effects on optical and optoelectronic properties was investigated.The combination effect of formed SiNWs and stain etching treatment in acid (HF/HNO₃/H₂O) solution on the surface morphol. of Si wafers as well as on the optical and optoelectronic properties especially a PL response at 640 nm are presented.As a results, the effective lifetime (τ_eff) and surface recombination velocity (S_eff) evolution of SiNWs after stain etching treatment showed significant improvements and less than 1% reflectance was achieved over the wavelength range of 400-800 nm and more than 36% reduction was observed compared to untreated surface.It has, thus, been demonstrated that all these factors may lead to improved energy efficiency from 8% to nearly 14.2% for a cell with SiNWs treated in acid (HF/HNO₃/H₂O) solution