Enhancing the optoelectronic properties of solution-processed AgInSe2 thin films for application in photovoltaics

AgInSe2 is a promising direct bandgap thin-film material with a rare n-type conductivity. Similar to thin film photovoltaic materials such as Cu(In,Ga)Se-2 (CIGSe), which have achieved efficiencies as high as similar to 23%, AgInSe2 also crystallizes in a chalcopyrite phase while also being more tolerant to antisite defects due to higher defect formation energies resulting from more significant variations in cation sizes. AgInSe2 has a suitable bandgap of 1.24 eV, which lies in the high-efficiency region of the detailed balance limit. In this work, we have utilized a dimethyl formamide-thiourea-chloride-based solution-processed route to deposit a thin film of AgInS2 which is converted into AgInSe2 after a heat-treatment step in a selenium environment. We observed that AgInSe2 optoelectronic properties depend on the Ag/In ratio and the selenium heat-treatment conditions. Significant improvements in photoluminescence yield and lifetime are observed for Ag-poor films in selenium-rich conditions. X-ray photoelectron spectroscopy (XPS) measurements confirm a higher amount of selenium on the surface of films with improved optoelectronic properties. Furthermore, a high minority carrier lifetime of 9.2 ns and a photoluminescence quantum yield (PLQY) of 0.013% are obtained without any passivating layer, which improved to 0.03% after CdS passivation. Hall effect measurements confirm that AgInSe2 has n-type conductivity with a moderate carrier concentration (10(-14) cm(-3)), more suitable for a p-i-n architecture. XPS has further confirmed the moderate n-type conductivity.