Elaboration and characterization of CuInSe2 thin films using one-step electrodeposition method on silicon substrate for photovoltaic application

Abstract

Bifacial solar cells combining a heterojunction cell on the upper side and crystalline silicon (c-Si) homojunction on the backside are very interesting devices to a more efficient use of the solar radiation. Cu(In,Ga)Se2(n)/c-Si(p)/c-Si(n+) or CuInSe2(n)/c-Si(p)/c-Si(n+) are very attractive heterojunctions to reach this target. In this work, a novel attempt has been made to grow CuInSe2 thin films on p-Si (100) substrate using one-step electrodeposition route with galvanostatic mode. The as-deposited samples were amorphous by nature which implies a rapid thermal annealing step. The effect of annealing temperature on the structural, morphological, optical and electrical properties of the fabricated hetero-structure CuInSe2/c-Si (100) was investigated by x-ray diffraction (XRD), scanning electron microscopy, energy dispersive spectroscopy (EDS) and UV-visible spectroscopy. XRD indicates that CuInSe2 films having single phase chalcopyrite with tetragonal crystal structure are obtained at 350 °C. Values of energy band gap of films at various annealing temperature were estimated to be in the range 0.94-1.01 eV. The optical parameters such as refractive index n(λ) and extinction coefficient k(λ) were estimated using an appropriate optical model. The AM1.5 current density-voltage characteristic of the fabricated Al/CuInSe2/c-Si (100) hetero-junction solar cell exhibits a short-circuit current density J sc of 4.06 mA cm-2, an open circuit voltage V oc of 0.28 V, a fill factor FF of 36.72% and a solar conversion efficiency η of 0.41%.