• Energy Research

Abstract In the fabrication of CuInS2/In2S3 solar cell using chemical spray pyrolysis (CSP) deposition technique, one of the major problems is the diffusion of Cu towards the In2S3 layer affecting stability and repeatability of the CuInS2/In2S3 cells. In order to ensure a Cu-free In2S3 layer, a ‘double layer structure’ of CuInS2 film, having a Cu-rich first layer and In-rich second layer was deposited using manual CSP technique. In this paper, we present the difference in material properties of single and double layered CuInS2 films and the results of characterisation of the junctions prepared using such films with β-In2S3 films. Better crystallinity as well as larger and densely packed grains were observed for the CuInS2 films having ‘double layer structure’. Such samples also possessed two band gaps, which was not due to the presence of different phases, but due to the Cu-rich and Cu-poor layers. In addition, their low resistivity makes the double layered CuInS2 film more beneficial for photovoltaic applications.

AbstractThin film solar cells having structure CuInS2/In2S3 were fabricated using chemical spray pyrolysis (CSP) technique over ITO coated glass. Top electrode was silver film (area 0.05cm2). Cu/In ratio and S/Cu in the precursor solution for CuInS2 were fixed as 1.2 and 5 respectively. In/S ratio in the precursor solution for In2S3 was fixed as 1.2/8. An efficiency of 0.6% (fill factor -37.6%) was obtained. Cu diffusion to the In2S3 layer, which deteriorates junction properties, is inevitable in CuInS2/In2S3 cell. So to decrease this effect and to ensure a Cu-free In2S3 layer at the top of the cell, Cu/In ratio was reduced to 1. Then a remarkable increase in short circuit current density was occurred from 3mA/cm2 to 14.8mA/cm2 and an efficiency of 2.13% was achieved. Also when In/S ratio was altered to 1.2/12, the short circuit current density increased to 17.8mA/cm2 with an improved fill factor of 32% and efficiency remaining as 2%. Thus Cu/In and In/S ratios in the precursor solutions play a crucial role in determining the cell parameters.

Abstract Thin films of Cu2ZnSnS4, a potential candidate for application as absorber layer in thin film solar cells, were successfully deposited on soda lime glass substrates using spray pyrolysis and the effect of variation of precursor on the structural and opto-electronic properties was investigated. We used stannous as well as stannic chloride as precursors of tin in the spray solution. All the films exhibited kesterite structure with preferential orientation along the (1 1 2) direction. But crystallinity and grain size were better for stannic chloride based films. Also they possessed a direct band gap of 1.5 eV and the absorption coefficient was >104 cm−1. Carrier concentration and mobility could be enhanced and the resistivity reduced by two orders by using stannic chloride in spray solution. Junction trials were performed with CZTS films prepared using stannic chloride precursor as the absorber layer and indium sulfide as the buffer layer. XPS depth profiling of the junction was done. Formation of CZTS could be confirmed and also information about the junction interface could be obtained from the XPS results. We obtained an open-circuit voltage of 380 mV and short-circuit current density of 2.4 mA/cm2.