The Roles of Poly(Ethylene Oxide) Electrode Buffers in Efficient Polymer Photovoltaics

Abstract

The role of poly(ethylene oxide) polymer is investigated as an effective buffer with Al electrodes to markedly improve the electrode interface and enhance the open‐circuit voltage (VOC) and the power conversion efficiency (PCE, η) of poly(3‐hexylthiophene) (P3HT):[6,6]‐phenyl C61‐butyric acid methyl ester (PCBM)‐based bulk‐heterojunction (BHJ) solar cells. A unique process is developed by thermally co‐evaporating the poly(ethylene glycol) dimethyl ether (PEGDE, Mn ca. 2000) polymer with Al metal simultaneously at different ratios in vacuum (10−6 Torr) to prepare the electrode buffers. The instant formation of a carbide‐like junction at the ethylene oxide/Al interface during the thermal evaporation is of essential importance to the extraction of electrons through the Al electrode. The performance of P3HT:PCBM‐based solar cells can be optimized by modulating the co‐evaporation ratios of the PEGDE polymer with Al metal due to the changes in the work functions of the electrodes. The VOC and η for devices fabricated with Al electrode are 0.44 V and 1.64%, respectively, and significantly improve to 0.58 V and 4.00% when applying the PEGDE:Al(2:1)/Al electrode. This research leads to a novel electrode design – free of salts, additives, complicated syntheses, and having tunable work function – for fabricating high‐performance photovoltaic cells.

A Versatile Buffer Layer for Polymer Solar Cells: Rendering Surface Potential by Regulating Dipole

“…P(VDF‐HFP) solution (1 mg mL −1 ) is spin‐coated on thermally annealed active layers with a thickness of 5 nm (Figure S2, Supporting Information). A reference device without CBL has an average PCE of 1.9%, which is similar to values of 1.64% and 1.98% reported earlier. After insertion of P(VDF‐HFP) layer, the PCE distinctly increases to 3.3%, which is even higher than the value of 3.1% obtained from the device with LiF as CBL ( Figure ).…”

Thermal metal deposition induces segregation in polymer thin films: a demonstration on OPVs

“…[3][4][5] Importantly, the performance of these devices was found to critically depend on the molecular interactions at the polymer/ metal interface. 10 A similar increase in performance was observed when the PEG was blended in solution with the P3HT:PCBM prior to spin coating. Here, we suggest that introducing the new polymer/metal interface during metallization could overcome the free surface energy consideration and alter the polymer surface composition.…”

Poly(3-hexylthiophene): synthetic methodologies and properties in bulk heterojunction solar cells

“…Upon blending the regioregular polymers with PCBM in chloroform, the hole mobilities were found to be typically reduced by one order of magnitude with respect to (112) the corresponding pristine P3HTs, and they did not significantly change upon thermal annealing. Next, very high regioregularity led to a faster (m $ 10 À5 cm 2 V À1 s À1 ) and almost balanced charge transport of the holes and electrons, and medium regioregularity resulted in lower (m $ 10 À4 cm 2 V À1 s À1 ) and unbalanced charge transport in the blends.…”