Enhancement of the photovoltaic properties of Ag2BiI5 by Cu doping

Abstract

Cu-doped Ag2BiI5 (Cu:SBI) powders with 0-10 mol% doping concentrations were synthesized by a solid-state method in an evacuated glass tube. While Cu doping did not appreciably modify the crystallographic structure or the bandgap of Ag2BiI5 (SBI), it significantly increased light absorption in the wavelength range of 400-700 nm. They were applied as light absorbers of n-i-p type solar cells employing mesoporous TiO2 as an electron transporting layer and PTAA as a hole transporting layer, and it was found that Cu doping leads to a notable increase in power conversion efficiency (PCE). Particularly, solar cell devices with 2.5 mol% Cu-doped SBI (SC-Cu2.5:SBI) exhibited a PCE of 2.53% with a V-OC of 619 mV, J(SC) of 7.13 mA cm(-2) and FF of 57.25%, which was increased by 25% compared with that of a bare SBI device (PCE = 2.04%). The PCE increase was mainly due to the significant increase in J(SC), suggesting that the enhancement is caused by the increase in light absorption. The effect of Cu dopants on the light absorption properties was investigated by first-principles calculations of energy band structures, and charge transport and recombination behaviors of Cu2.5:SBI were analyzed by transient absorption spectroscopy. Under high humidity conditions, SBI shows much better long-term stability than Pb-perovskites such as methylamine lead iodide, while SC-Cu2.5:SBI shows comparable stability to the bare SBI-based device, implying that Cu doping does not influence the stability of SBI.