Abstract
The continuous thin film of silver (Ag) film is important for semitransparent electrodes in polymer solar cells, while the Ag atoms form as non-continuous below a critical thickness. Here, semitransparent inverted polymer solar cells were fabricated using thermally evaporated Ag/germanium (Ge)/Ag as highly transparent electrodes. An ultra-thin Ge film was introduced to modify the growth mode of Ag. The dependence of the device performance and the thickness of the outer Ag film was investigated. Ag/Ge/Ag electrodes exhibited excellent optical and electrical properties, which were proved by the transmittance and reflectance spectra. A champion efficiency of 5.1% was achieved with an open-circuit voltage level of 0.703 V, a short current density of 11.63 mA/cm2, and a fill factor of 63%. The average visible transmittance (300–800 nm) of devices with Ag/Ge/Ag was calculated as 25%.
Highlights
Polymer solar cells (PSCs) show strong competitiveness in future energy sources due to their solution processing, large area printing, easy manufacturing, flexibility, and low material costs [1,2,3,4,5,6,7,8,9,10,11,12,13]
The power conversion efficiency (PCE) level has exceeded 18% due to the progress made in bulk heterojunction solar cells [14,15]
The work function (WF) of the Ag/Ge/Ag film was calculated through ultraviolet photoelectron spectra (UPS) measurement using He I radiation
Summary
Polymer solar cells (PSCs) show strong competitiveness in future energy sources due to their solution processing, large area printing, easy manufacturing, flexibility, and low material costs [1,2,3,4,5,6,7,8,9,10,11,12,13]. Ag film deposited on the substrate initially produced isolated islands and formed non-continuous clusters below this thickness. These islands joined together and resulted in a continuous Ag film. A thin gold film was introduced by Li et al to obtain a single-layer, semitransparent electrode [26]. Despite their excellent transmittance, these solar cell devices suffer from some inherent drawbacks, such as high series resistance and low FF [27,28,29]. The dependence of device performance on the thickness of each layer was investigated; the transmittance, reflectance, and color-neutrality of the different electrodes are analyzed through various thicknesses of the Ag capping layer
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