Achieving high efficiency silicon heterojunction solar cells by applying high hydrogen content amorphous silicon as epitaxial-free buffer layers

•High efficiency silicon heterojunction solar cell with no epitaxial growth.•Appling a high hydrogen content a-Si:H film as epitaxial-free buffer layer.•The high hydrogen content a-Si:H film shows superior passivation quality.•Correlation between hydrogen content of a-Si:H film and cell performance reveled. High hydrogen content (CH) intrinsic amorphous silicon (a-Si:H) buffer layers were deposited on both sides of crystalline silicon wafers using plasma-enhanced chemical vapor deposition technique, which significantly improved surface passivation as well as conversion efficiency of the silicon heterojunction solar cells. Properties of the buffer layer and impact on the device performance were investigated. High resolution transmission electron microscope characterization shows that no obvious epitaxial growth occurred at the interface as long as a-Si:H buffer layer was introduced between c-Si and bulk intrinsic layer. Further study indicates that minority carrier lifetime of the device is related to hydrogen content of the buffer layer, reaching highest value up to 2050 ms at CH of 33%. These findings evidently confirmed that suppression of epitaxial growth and thus improved passivation were realized by using high-hydrogen-content a-Si:H buffer layer, based on which a high efficiency solar cell was prepared with large area.