A cadmium sulfide / cadmium telluride (CdS/CdTe) solar cell consists of thedevice stack: Glass substrate / SnO2:F (TCO, transparent conductive oxide) / CdS (n-type semiconductor) / CdTe (p-type semiconductor) / Cu/Au (metal/back contact). During the fabrication process of the CdS and CdTe thin films pinholes are usually formed within these layers (random defects, which are entropy driven). After the semiconductor deposition, and subsequent heat treatments, the solar cell is completed with the deposition of a metal electrode onto the CdTe surface. The presence of a pinhole through the semiconductor layers leads to the formation of a wire like connection through the photovoltaic device (shunt, metal connection of the TCO and metal electrodes), which adversely affects the overall performance of the solar cell. Our proposed solution is to fill these pinholes with a resistive material such as polyaniline, using an electrochemical deposition (electrochemical polymerization) technique. The electrochemical deposition technique is performed by applying a voltage across a conductive substrate (TCO coated glass) and an inert electrode (Pt), both placed inside an electrolyte rich solution containing aniline. The aniline monomer then reacts at the positively charged conductive
substrate to form a polymer (polyaniline). After the polyaniline film deposition, this new layer acts as an insulating layer, preventing the back contact (Cu/Au) from electrically contacting the TCO layer, thus avoiding shunting of the solar cell. Characterization techniques employed in this study are: depth profilemeter, x-ray photoelectron spectroscopy, electron spray ionization - mass spectrometry, scanning electron microscopy, energy dispersive spectroscopy and grazing angle incidence x-ray diffraction. Subsequently, this technique is applied to CdTe solar cells that have pinholes and on an artificially scribed pinhole. After the electro deposition of polyaniline the CdTe solar cell is completed by metalizing using a Cu-Au back contact, and characterized by JV-measurements, under AM1.5 (terrestrial spectrum).
Thus, we were able to obtain promising results that indicate both the deposition
of the polymer on the device and hindrance of shunting of the CdTe solar cell.