Scientists at the German research centre Forschungszentrum Juelich GmbH have created a heterojunction silicon solar cell that has no transparent conducting oxide (TCO) at its front contacts.
TCO is a transparent and conductive material that has been used for decades on both sides of contact crystalline silicon (C-Si) heterojunction (SHJ) solar cells to provide transverse conductivity to collect charge carriers. "Our latest study shows that Ag contact or Al contact may be candidate materials for TCO-free SHJ solar cells with efficiencies of over 22%," researcher Shenghao Lee told PV Magazine. "So far, we have not carried out a cost assessment of this type of solar cell. In the first step of the proof of concept, we used tin, aluminium and silver (Ti/Au/Ag) as contact metals, which is not ideal for mass production."
In the study published in Joule, studies of front contacts of non-transparent conductive oxides for high-efficiency silicon heterojunction solar cells show that TCO can ensure sufficient transverse conductivity, but it has good but imperfect transmission, resulting in losses. Short-circuit current density.
External quantum efficiency measurements show that the 2.0 × 2.0 cm2 cell has an efficiency of over 22%. "By replacing the TCO layer with a silicon nitride (SiNx) layer, a current gain of 0.99 mA/cm2 can be obtained," the researchers concluded. "In this design, the SHJ solar cell's dependence on indium is alleviated while avoiding design conflicts between the transparency and conductivity of the TCO layer."