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Silicon nanowire (SiNW)-based solar cell fabrication was developed using a combination of diffused back surface field (BSF) formation and two-step H2 annealing for greater efficiency enhancement. Two different n-SiNW structures synthesized by metal-catalyzed electroless etching and nanoimprinting followed by Bosch process were used as substrates to fabricate single-junction solar cells with chemical vapor deposition grown p-Si shell layer. Without BSF formation, shell layer coverage of nanoimprinted SiNW solar cells fabricated using two-step H2 annealing was optimized and the H2 annealing effect on the shell layer crystallinity was investigated using transmission electron microscopy. Then, the effects of combined H2 annealing process for BSF formation together with shell layer treatment were observed under various annealing times. Enhancement of ∼1.5% absolute efficiency of both SiNW-based solar cells was achieved. Reduction of carrier recombination by BSF layer accompanied with the reduction of the defect density on n-SiNW surfaces and inside p-Si layer could be accomplished.