CO2 plasma treatment to promote crystallinity of p-type emitter layer for the silicon heterojunction solar cells

To improve the properties of the emitter layer so as to prompt the performance of the silicon heterojunction (SHJ) solar cells, we have implemented the CO2 plasma treatment on i-a-Si:H/p-type emitter interface. Its effect on the electrical, optical, and structural properties as well as passivation characteristics of the p-type emitter layer is investigated. Using this kind of nuclear-induced treatment, the conductivity of the emitter is remarkably improved and increases by 6–8 orders of magnitude. And the optical band gap E04 of p-type layer increases and can be tuned between 1.98 and 2.04 eV, depending on the treatment time. In addition, due to the doping of oxygen into the a-Si:H film, the treatment makes the total surface passivation degrade. As a result, the open-circuit voltage and short-circuit current of the SHJ solar cell both decrease slightly. However, owing to improving p-type layer, the Fill Factor and conversion efficiency of the solar cell with the CO2 plasma treatment enhance obviously. This work provides an effective way of improving the properties of the emitter layer of the SHJ solar cells and thus to improve their efficiency.