Effects of the photoactive layer properties and current transmission mechanism on optical and electrical characteristics of organic photovoltaic

The P3HT:PCBM is an important organic material as an active layer for bulk heterojunction (BHJ) organic photovoltaics (OPVs). However, in terms of photophysical properties, blend ratios of both materials and device design is an important parameter for OPVs devices. In this study, the P3HT: PCBM photoactive layer, blended in different proportions by mass (1:1, 1:0.8, 1:0.6) was coated on the PEDOT:PSS surface using the spin coater method for different devices. Finally, Al have been evaporated on the photoactive layer and the device structure completed. In other examples, 2 nm lithium fluoride (LiF) as buffer layer evaporated on the active layer for each blending ratio before metal. Optical absorption, AFM, XRD, Raman and XPS measurements were taken for each active layer and it was observed that the surface morphology and absorption characteristic of the active layer changed according to the mixing ratios. This change in active layer properties directly affected the device parameters. Electrical characterization of the six different devices performed with current density-voltage (J-V) measurement and by used a solar simulator under 100 mW/ cm2 irradiation intensity. Depending on the increase in short circuit current density (Jsc) and open current voltage (Voc) values in the devices, the power conversion efficiency (PCE) of the OPVs obtained varied between 0.86% and 2.74%. This change can be attributed to the fact that the P3HT:PCBM photoactive layer forms a smoother surface morphology depending on the PCBM ratio and the series resistance decreases. Another reason for this change in PCE can be explained by the effective electron injection of the LiF layer, LiF/Al layer with lower work function and less carrier deposition at its metal-active layer interfaces. It result has been obtained that the active layer with a ratio of 1:0.8 has a more homogeneous surface morphology and the series resistance decreases, the presence of the LiF layer in the device structures increases the Jsc and Voc, accordingly the PCE increases to 2.74%. These results showed that BHJ OPV with high PCE can be obtained with the ideal mixing ratio and appropriate device design.

Automated summary

The study utilized P3HT:PCBM photoactive layers blended in different ratios and observed that the mixing ratio affected the surface morphology and absorption characteristics of the active layer, thereby impacting the device performance parameters. By evaporating a LiF layer on the active layer and optimizing device design, the power conversion efficiency of OPVs was successfully increased.