Dielectric-Based Rear Surface Passivation Approaches for Cu(In,Ga)Se2 Solar Cells—A Review

Abstract

This review summarizes all studies which used dielectric-based materials as a passivation layer at the rear surface of copper indium gallium (di)selenide, Cu(In,Ga)Se2, (CIGS)-based thin film solar cells, up to 2019. The results regarding the kind of dielectric materials, the deposition techniques, contacting approaches, the existence of additional treatments, and current–voltage characteristics (J–V) of passivated devices are emphasized by a detailed table. The techniques used to implement the passivation layer, the contacting approach for the realization of the current flow between rear contact and absorber layer, additional light management techniques if applicable, the solar simulator results, and further characterization techniques, i.e., external quantum efficiency (EQE) and photoluminescence (PL), are shared and discussed. Three graphs show the difference between the reference and passivated devices in terms of open-circuit voltage (Voc), short-circuit current (Jsc), and efficiency (η), with respect to the thicknesses of the absorber layer. The effects of the passivation layer at the rear surface are discussed based on these three graphs. Furthermore, an additional section is dedicated to the theoretical aspects of the passivation mechanism.

Challenges and opportunities for an efficiency boost of next generation Cu(In,Ga)Se2 solar cells: prospects for a paradigm shift

“…Promising results for back surface passivation were achieved by the use of different approaches based on atomic layer deposition techniques of different materials. 44 It could be also considered to tune the band offsets of CIGS by alloying, for example with Ag. 45 The use of III-V materials was also proposed as a possible route for selective contacts.…”

High‐Performance and Industrially Viable Nanostructured SiOx Layers for Interface Passivation in Thin Film Solar Cells

“…[ 18 ] One approach to mitigate the recombination in the rear CIGS surface is focused on the use of an insulator passivation layer, in between the rear contact and the CIGS layer. [ 18,19,20-28 ] To establish electrical contact between CIGS and the rear electrode, nanocontacts are opened in the insulator layer, with e‐beam lithography being commonly used. [ 4,18,19,29 ] However, photolithography has the advantage of being cheaper and to have higher machine throughput compared with e‐beam lithography.…”

“…Several insulator materials, e.g., Al 2 O 3 , Si 3 N x , SiO x , TiO 2 , to name but a few, have been studied as passivation layers in the CIGS technology. [ 20,25,30-33 ] The prospect of using the same approach and insulator to passivate both front and rear interfaces of the same solar cell is very attractive from a fabrication perspective, and SiO x emerges as a strong material to perform such role. [ 20,30,34 ] SiO x presents promising properties that allow for its implementation as front and rear passivation layers, namely, the ability to change the polarity values of the fixed insulator charges ( Q f ) by manipulating the deposition parameters, enabling an efficient field‐effect passivation of both minority and majority CIGS charge carriers.…”

Ultrathin CIGSe Solar Cells with Integrated Structured Back Reflector

“…[ 1–4 ] However, this requires a very low back contact recombination velocity and advanced optical light management. The standard molybdenum back contact is generally attributed with a high recombination velocity [ 5–7 ] and has a poor optical reflectivity. [ 8 ] In ref.…”