Silver-promoted enhanced optoelectronic properties of wide bandgap (Ag,Cu)(In,Ga)S2 for thin film solar cells |
Arivazhagan Valluvar Oli, Michele Melchiorre, Kulwinder Kaur, Susanne Siebentritt University of Luxembourg, Luxembourg, --, Luxembourg |
Environmentally stable, wide bandgap (>1.55 eV) and inorganic sulfide chalcopyrite with the composition of Cu(In,Ga)S2 (CIGS) has interesting potential as a top cell in tandem photovoltaics. Herein, CIGS absorbers are alloyed with Silver (Ag), to form ACIGS, to enhance the structural and optoelectronic properties. Ag promotes the growth of larger grains and reduces the grain boundaries. The lower melting temperature of the alloy accelerates the diffusion of elements leading to improved crystallinity of ACIGS without phase splitting as evident from X-ray diffraction. The Quasi-Fermi level splitting (ΔEF) determined from the 1 sun absolute PL spectroscopy using PL quantum yield approach shows 1.03 eV which is 50 meV higher than reference CIGS. The ACIGS further exhibits effective minority charge carrier lifetime (𝛕eff), calculated based on weighted average method, close to 7 ns as determined from time resolved PL spectroscopy (TRPL). The slow decay component of ACIGS from TRPL shows over 28 ns while CIGS shows 12 ns. The hole doping density is calculated based on ΔEF and 𝛕eff, and its impact on the optoelectronic properties of the absorber is discussed. The solar cells based CIGS and ACISG are expected to be fabricated and presented. |