Solution combustion synthesis of transparent conducting thin films for sustainable photovoltaic applications

Abstract

Sunlight is arguably the most promising continuous and cheap alternative sustainable energy source available at almost all living places of the human world. Photovoltaics (PV) is a process of direct conversion of sunlight into electricity and has become a technology of choice for sustainable production of cleaner and safer energy. The solar cell is the main component of any PV technology and transparent conducting oxides (TCO) comprising wide band gap semiconductors are an essential component of every PV technology. In this research, transparent conducting thin films were prepared by solution combustion synthesis of metal oxide nitrates wherein the use of indium is substituted or reduced. Individual 0.5 M indium, gallium and zinc oxide source solutions were mixed in ratios of 1:9 and 9:1 to obtain precursor solutions. Indium-rich IZO (A1), zinc-rich IZO (B1), gallium-rich GZO (C1) and zinc-rich GZO (D1) thin films were prepared through spin coating deposition. In the case of A1 and B1 thin films, electrical resistivity obtained was 3.4 × 10−3 Ω-cm and 7.9 × 10−3 Ω-cm, respectively. While C1 films remained insulating, D1 films showed an electrical resistivity of 1.3 × 10−2 Ω-cm. The optical transmittance remained more than 80% in visible for all films. Films with necessary transparent conducting properties were applied in an all solution-processed solar cell device and then characterized. The efficiency of 1.66%, 2.17%, and 0.77% was obtained for A1, B1, and D1 TCOs, respectively, while 6.88% was obtained using commercial fluorine doped SnO2: (FTO) TCO. The results are encouraging for the preparation of indium-free TCOs towards solution-processed thin-film photovoltaic devices. It is also observed that better filtration of precursor solutions and improving surface roughness would further reduce sheet resistance and improve solar cell efficiency.