Silicon heterojunction solar cells: Optimization of emitter and contact properties from analytical calculation and numerical simulation

Role of the Front Electron Collector in Rear Emitter Silicon Heterojunction Solar Cells

“…In consequence, a high band bending, i.e., an accumulation of electrons close to the interface, is necessary to assure a high effective minority carrier lifetime, especially at low injection levels. Similar effects were already observed on the hole collector side, where, depending on the TCO work function, a thick and highly doped (p)a-Si:H is required to achieve high V oc values [19]: When (n)a-Si:H is thinner than its Debye screening length L D defined by the defect density at the Fermi level N(E F ), L D = ∈ /q 2 N (E F ), both space charge regions interplay, and (n)a-Si:H is depleted [19], [20]. Regarding electron transport, from the equilibrium band diagram, one sees that electrons coming from the substrate have Fig.…”

“…Interfacial defects are present in a thin defective c-Si layer yielding an equivalent interface density of 10 9 cm −2 . More details about Afors-Het simulations can be found in [19]. In Fig.…”

Investigation of selective junctions using a newly developed tunnel current model for solar cell applications

“…Richter's Auger recombination model is accounted for, as it has recently been implemented in AFORS-HET (see Appendix B) [33]. On the back side, an (n)a-Si:H back surface field is introduced; for a-Si:H material parameters see reference [34]. No interface defects are considered on the back side.…”

“…Interface defects between the (n)c-Si absorber and the (p)c-Si hole collector were taken into account by the introduction of a 1 nm c-Si layer with the same properties as the absorber, but with a high concentration of defects. Details on such a defect layer can be found in [34]. On both the front and back side, the contact work function to the external circuit was set at the same values as the contacted semiconductors, such that a contact with flat band conditions in the dark, with Ohmic IV characteristics is formed.…”

Molybdenum and tungsten oxide: High work function wide band gap contact materials for hole selective contacts of silicon solar cells

“…Their low net doping and high defect density make the optimization of the hole contact typically more challenging than that of the electron contact. As a minimum thickness (and doping) of the a-Si:H has to be a applied to form the junction [9,10] (ii), the parasitic photon absorption in the doped a-Si:H lowers the carrier generation in the absorber significantly [11]. (iii) The temperature stability of a-Si:H is limited to below 200°C [12], which calls for adapted process steps for back end processing (TCO, metallization) and module integration, both of which are hardly compatible with the well-established mainstream processes used for homojunction cells.…”