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.