Thin film solar cells with extremely thin absorber layer having multiple absorption bands: A novel attempt

• CSP technique was used to deposit a new multiple band gap absorber.
• Both CuInS2 and Cu2S are utilized as absorber.
• Absorber was deposited simply by reducing In concentration in CuInS2 precursor.
• ETA solar cell with 3.82% efficiency was achieved with the new absorber layer.
• Easy substitute for the tandem solar cells for absorption of multiple wavelengths.

Chemical Spray Pyrolysis (CSP) technique was utilized for depositing ‘Extremely Thin Absorber (ETA)’ layer solar cells having phases of both CuInS2 and Cu2S in the absorber, so as to have multiple band gaps of 1.45 eV and 1.80 eV respectively. Cell fabricated using this absorber is almost equivalent to a tandem cell capable of absorbing photons of two energies. This was achieved simply by lowering concentration of indium in conventional CuInS2. Presence of both CuInS2 and Cu2S phases were confirmed through X-ray diffraction and Raman studies. Multiple absorptions in the film were evident from the absorption spectra. Also the ‘CuInS2:Cu2S’ absorber was used for the fabrication of ETA solar cell with structure ITO/(CuInS2:Cu2S)/In2S3/Ag. Comparing with performance of ITO/CuInS2/In2S3/Ag solar cells, they exhibits 17%, 15% and 47% increases in short circuit current, fill factor and efficiency respectively. The best device realized in this study has open circuit voltage of 518 mV and short circuit current density of 14.25 mA/cm2. Efficiency and fill factor were 3.82% and 52% respectively.

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