The Influence of Deposition Rates on Properties of AlPcCl Thin Films and on the Performance of Planar Organic Solar Cells

Abstract

The performance of organic photovoltaic cells depends on different properties of the organic materials, such as carrier mobility, band structure, morphology, and crystallinity. For AlPcCl, it is shown that these properties are dependent on the layer deposition rates. As the deposition rate increases, the surface roughness of AlPcCl layers decreases. In contrast, the crystallinity of the layers increases as the deposition rate decreases, thereby increasing the hole mobility value. These effects are opposed: the former effect allows higher open circuit voltages to be obtained as the deposition rate increases, whereas the latter increases the short circuit current as the deposition rate decreases. Therefore, there is a trade‐off between open and short circuit current values, and it is necessary to find the best deposition rate for AlPcCl. Here, it is shown that the highest mobility carriers in layers deposited slowly allow the use of thicker AlPcCl layers, which permits acceptable open circuit voltage values and optimum photovoltaic cell efficiencies to be obtained. This results in an optimum efficiency value of 3.97% for a 26‐nm‐thick AlPcCl film that is deposited at 0.02–0.03 nm s−1.

On the contribution of fullerene to the current of planar heterojunction organic solar cells

“…For higher deposition rate, the V oc and FF values and the reproducibility of the results decrease. It was also shown that the optimum thickness of the SubPc layer was 16 nm, for smaller or higher thickness the OPV efficiency decreases [16]. At the beginning of the present work, even after optimization of the deposition rate and film thickness of SubPc, some variations in V oc and FF values persist.…”

“…Therefore, knowing that for classical cells the configuration was Glass/ITO/MoO 3 /SubPc/C 60 /Alq 3 /Al, for reverse structures we used the configuration Glass/ITO/Alq 3 /C 60 /SubPc/MoO 3 /Al. We have already shown that, in the case of inverted OPVs it was difficult to achieve reproducible performances [16]. Actually, it was demonstrated that the open circuit voltage (V oc ), the fill factor (FF) and therefore the OPV efficiency (η) depend on the morphology of the SubPc layer, which itself depends on its deposition rate.…”