Hybrid solar cells based on CuInS2 and organic buffer-sensitizer layers

Hybrid solar cells on the basis of CuInS₂ (CIS) photoabsorber on Cu-tape (CISCuT) in combination with organic buffer layers of Zn-phthalocyanine (ZnPc), ZnPc:fullerene (ZnPc:C₆₀) composite and conductive polymer buffer layers of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonate (PSS) were prepared using vacuum evaporation and spin-casting techniques. To prepare solar cells with an active area of 2 cm², the appropriate deposition parameters and thickness of ZnPc, ZnPc:C₆₀ and PEDOT-PSS layers were selected experimentally. For preparation of semitransparent contact-window layers, chromium and gold were evaporated on the surface of ZnPc, ZnPc:C₆₀ and PEDOT-PSS films. It was found that an intermediate chromium layer improves PV properties of the structures with organic buffer layers. The photosensitivity at small illumination intensities of complete structures with ZnPc and ZnPc:C₆₀ layers increased more than one order of magnitude in comparison with the structures where the PEDOT-PSS buffer layer was deposited. The presence of C₆₀ in the composite-buffer layer results in increased photoconductivity. The best structure with composite ZnPc:C₆₀ buffer layer showed an open-circuit voltage of 560 mV, a short-circuit current density of around 10 mA/cm² and a photoconversion efficiency of around 3.3% under the light illumination with an intensity of 100 mW/cm² from a tungsten-halogen lamp. The low transmission of the semitransparent chromium-gold window layer is the reason for relatively low current density.