High-efficiency inverted polymer solar cells controlled by the thickness of polyethylenimine ethoxylated (PEIE) interfacial layers

Abstract

In this work, we investigate the effect of the thickness of the polyethylenimine ethoxylated (PEIE) interface layer on the performance of two types of polymer solar cells based on inverted poly(3-hexylthiophene) (P3HT):phenyl C61-butryric acid methyl ester (PCBM) and thieno[3,4-b]thiophene/benzodithiophene (PTB7):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM). Maximum power conversion efficiencies of 4.18% and 7.40% were achieved at a 5.02 nm thick PEIE interface layer, for the above-mentioned solar cell types, respectively. The optimized PEIE layer provides a strong enough dipole for the best charge collection while maintaining charge tunneling ability. Optical transmittance and atomic force microscopy measurements indicate that all PEIE films have the same high transmittance and smooth surface morphology, ruling out the influence of the PEIE layer on these two parameters. The measured external quantum efficiencies for the devices with thick PEIE layers are quite similar to those of the optimized devices, indicating the poor charge collection ability of thick PEIE layers. The relatively low performance of devices with a PEIE layer of thickness less than 5 nm is the result of a weak dipole and partial coverage of the PEIE layer on ITO.

Long-Term Stable Organic Photodetectors with Ultra Low Dark Currents for High Detectivity Applications

“…The low dark current values confirm a full PEIE surface coverage on ITO. At higher concentrations, we still observe low dark current values but the thicker PEIE layer increases the contact resistance that prevents photo-generated charge extraction32. In contrast, for lower concentrations our results show that despite low values of WF, higher dark current densities are observed.…”

Organic solar cells and fully printed super-capacitors optimized for indoor light energy harvesting

“…Here, the thickness of the PEIE layer is varied in order to control the shunt resistance and optimize the organic solar cells for indoor light. Previous studies [40], [41] have shown that PEIE is an insulator which can modify the series resistance and the work function of the cathode as a function of its thickness. PEIE thickness has also been shown to influence the reverse bias saturation dark current in organic photodiodes.…”

“…The series resistance value of the thin PEIE cell is close to that of a device with no PEIE (direct contact between the active layer and aluminum). Therefore, it can likely be attributed to a less than optimal charge extraction due to too thin of a layer [41]. On the other hand, the thick PEIE cell has a slightly higher series resistance than the medium PEIE cell, suggesting that the insulating nature of the PEIE starts to be impactful.…”

PEIE capped ZnO as cathode buffer layer with enhanced charge transfer ability for high efficiency polymer solar cells

“…Polyethylenimine ethoxylated (PEIE) has been widely used as interface modified layer in in organic light emitting diodes and organic solar cells [32][33][34][35][36][37][38][39]. Zhou et al [34] has used PEIE to reduce the work function of metals as well as oxide electrodes.…”