KF Postdeposition Treatment in N2 of Single-Stage Thin Cu(In,Ga)Se2 Absorber Layers

Jessica De Wild,Jef Poortmans,Guy Brammertz,Thierry Kohl,Marc Meuris,Gizem Birant,David Mate Parragh,Bart Vermang,Dilara G Buldu

doi:10.1109/jphotov.2019.2947758

Abstract

Thin (<;500 nm) single-stage coevaporated Cu(In, Ga)Se 2 absorber layers are treated with a KF postanneal in N 2 atmosphere. The conditions of the postanneal initial acceptor concentration and the temperature are varied. Solar cells are characterized with current-voltage and capacitance-voltage measurements. Efficiencies up to 12% with an open-circuit voltage (V oc ) of >640 mV were achieved after the KF treatment. From SCAPS simulations and temperature dependent current voltage measurements, it is concluded that the V oc of these cells are limited by backcontact surface recombination and, thus, further improvements require passivation of the back contact.

Highlights

Thin film Cu(In,Ga)Se2 (CIGS) solar cells have reached an efficiency beyond 23%
In this contribution we investigate the effect of the KF post deposition treatment (KF-PDT) in N2 atmosphere on our thin ungraded absorber layers
KF-PDT was performed on single-stage thin absorber layers in N2 atmosphere

Summary

INTRODUCTION

Thin film Cu(In,Ga)Se2 (CIGS) solar cells have reached an efficiency beyond 23%. when going to modules the efficiency is max 19% but often less [1]. We are aiming to achieve this by decreasing the thickness to ~ 500 nm and using an ungraded absorber layer grown with a single stage co-evaporation step This makes the process simpler, fast and requires less material. Since the thin layers are rather different in their compositional depth profile and grain size compared to the thicker 3-stage co-evaporated layers, re-investigation of some commonly used process steps like alkali addition is required. In this contribution we investigate the effect of the KF post deposition treatment (KF-PDT) in N2 atmosphere on our thin ungraded absorber layers. Efficiencies up to 12% are achieved with the new anneal method

EXPERIMENTAL DETAILS

Solar Cells

CONCLUSIONS