Improved Performance of Ultrathin Cu(InGa)Se<inline-formula><tex-math>$_{\bf 2}$</tex-math> </inline-formula> Solar Cells With a Backwall Superstrate Configuration

Abstract

A backwall superstrate device structure that outperforms conventional substrate Cu(In,Ga)Se 2 devices for thin absorbers is described. The backwall structure of glass/ITO/MoO 3 /Cu(In,Ga)Se 2 /CdS/i-ZnO/Ag utilizes a MoO 3 transparent back contact to allow illumination of the device from the back. The device performance has been improved by modifying the Cu(In,Ga)Se 2 , including alloying with Ag to form (AgCu)(InGa)Se 2 absorber layers. In addition, sulfized back contacts including ITO-S and MoS 2 are compared. Interface properties are discussed based on the XPS analysis and thermodynamics of reactions.Index Terms-(AgCu)(InGa)Se 2 , backwall structure, solar cell, thin film, transparent back contact.

Novel back contact reflector for high efficiency and double‐graded Cu(In,Ga)Se2 thin‐film solar cells

“…Similar observations in case of ITO back contacts were explained with an unfavorable band alignment between the absorber and the oxide layer . In contrast, samples B and C show diode behavior, confirming that a thin layer of Mo respectively MoSe x enables formation of a more ohmic contact as was reported before …”

“…15 In contrast, samples B and C show diode behavior, confirming that a thin layer of Mo respectively MoSe x enables formation of a more ohmic contact as was reported before. [15][16][17][18] Table 1. A difference of around 20 meV was found which is similar, or in case B even more than the observed reduction in V oc indicating that the V oc loss did not increase for cases B and C. In the following, these findings are discussed in view of more detailed optical and compositional characterizations.…”

“…Also, we study how thin Mo or MoSe x interlayers at the IZO/CIGS interface affect the device properties. Such interlayers were reported to be mandatory for growth on metal oxides to improve the interface resistance . Finally, Al was chosen because of the suitable optical properties and its expected benign effect in case that residual diffusion into the absorber layer would occur.…”

“…Such interlayers were reported to be mandatory for growth on metal oxides to improve the interface resistance. [15][16][17][18] Finally, Al was chosen because of the suitable optical properties and its expected benign 19 effect in case that residual diffusion into the absorber layer would occur. Figure 1 displays the different back contact designs considered here.…”

Chalcopyrite compound semiconductors for thin film solar cells

“…Therefore optical confinement is needed. This is achieved by optimising reflexion and absorption properties [46,47], by structures optimised for back side illumination [48,49] or by light trapping [50]. Light trapping can be achieved by using plasmonic structures: various approaches have been applied: Ag nanostructures at the back contact [51], at the surface of the cell [52], or at the surface of the absorber [53].…”