Low Temperature Aqueous Solution-Processed ZnO and Polyethylenimine Ethoxylated Cathode Buffer Bilayer for High Performance Flexible Inverted Organic Solar Cells

Abstract

]-phenyl-C 71 -butyric acid methyl ester (PTB-7:PC 71 BM) material systems. It is found that, compared with pure ZnO or PEIE cathode buffer layer (CBL), the proper combination of low-temperature processed ZnO and PEIE as the CBL enhanced the short circuit current density (J SC ), resulting in better device performance. The increased J SC results from the enhanced electron collection ability from the active layer to the cathode. By using the ZnO/PEIE CBL, a power conversion efficiency (PCE) as high as 4.04% for the P3HT:PC 61 BM flexible device and a PCE as high as 8.12% for the PTB-7:PC 71 BM flexible device are achieved, which are higher than the control devices with the pure ZnO CBL or pure PEIE CBL. The flexible inverted OSC also shows a superior mechanical property and it can keep 92.9% of its initial performance after 1000 bending cycles with a radius of 0.8 cm. These results suggest that the combination of the low temperature aqueous solution processed ZnO and PEIE can be a promising cathode buffer bilayer for flexible inverted OSCs.

In-depth analysis on PTB7 based semi-transparent solar cell employing MoO3/Ag/WO3 contact for advanced optical performance and light utilization

“…For this reason, fluorine-doped tin oxide (FTO) with high optical transmittance and conductivity and low work function (4.4 eV) was used as a transparent bottom contact material to allow more photons to reach the active region of the OSC from the bottom electrode side 40 . FTO offers superior optical transmittance (> 90%) across the entire VR regardless of fluorine doping 41 . Additionally, FTO can be fabricated at a lower cost than indium-doped tin oxide (ITO), which is often used in conventional structures, and its work function is less dependent on the cleaning procedure 40 .…”

“…ZnO has a conduction band energy of about − 4.4 eV and a valence band energy of − 7.4 eV. Owing to this band feature, electrons generated in the active region can be transported to ZnO, while holes can be blocked 41 . ZnO is also called the ETL in OSC due to this function.…”

Impact of ZnO Photoluminescence on Organic Photovoltaic Performance

“…ZnO is a typical n-type semiconductor with a band gap around 3.3 eV. , It is widely used as an electron transport layer (ETL) in the third generation solar cells, especially in organic photovoltaic (OPV) cells, − because of facile synthesis, solution processability, suitable energy levels, ,,− reasonable electrical conductivity, tunable semiconductor properties, and so forth. Over the years, a few synthetic protocols for ZnO nanoparticles (NPs) have been developed. ,− Different ZnO synthetic routes and conditions result in slightly different physical properties, such as dispersity, particle size, and photoluminescence (PL). ,,, Variation in photoluminescent colors arises from different forms of defects .…”

Inverted Organic Solar Cells with Low-Temperature Al-Doped-ZnO Electron Transport Layer Processed from Aqueous Solution

“…The aqueous-based Zn-ammine complex solutions represent one of the most promising routes to obtain the ZnO film at a low temperature due to the extremely low decomposition temperature [ 39 , 40 , 41 , 42 ]. This makes it possible to deposition the ZnO thin-film onto flexible substrates [ 43 , 44 ]. However, very different from the sol-gel method processed ZnO (where to dope the ZnO is relatively easy), to dope the ZnO film processed from the Zn-ammine complex solutions is difficult since the introduction of metal ions into the Zn-ammine complex is a nontrivial process as ammonium hydroxide tends to precipitate metal salts due to acid–base neutralization reaction.…”