Investigation of H 2 /CH 4 mixed gas plasma post-etching process for ZnO:B front contacts grown by LP-MOCVD method in silicon-based thin-film solar cells

Abstract A new plasma post-etching method, H 2 /CH 4 mixed gas plasma, is introduced to modify ZnO:B films grown by LP-MOCVD technique, successfully relaxing the double trade-offs, i.e., transparency/conductivity trade-off and surface texture/ V oc and FF trade-off. To deeply evaluate the post-etching process, optical emission spectroscopy technique is applied to diagnose the plasma condition. Upon different etching power, three distinct possible etching mechanisms are identified by analyzing the evolution of H α * , H β * , CH * emission species in the plasma space. It is demonstrated that H β * and CH * species are responsible for the physical etching process and chemical etching process, respectively, from which a new “soft” surface morphology is formed with a combination of micro- and nano-sized texture. Additionally, H α * species can bond with ZnO and also passivate the grains boundaries, thereby making both the carrier concentration and hall mobility increase. This process is defined as chemical bonding process. Finally, pin-type a-Si:H single-junction solar cells with an optimized device structure is grown on the etched ZnO:B substrate. The corresponding electrical parameters, such as J sc , V oc and FF, are simultaneously improved compared with the solar cell deposited on as-grown ZnO:B substrate with the same fabrication process. As a consequence, a noteworthy 8.85% conversion-efficiency is achieved with an absorber layer thickness only 160 nm.