Enhanced Performance in Inverted Polymer Solar Cells with D–π–A‐Type Molecular Dye Incorporated on ZnO Buffer Layer

Abstract

We report the superior characteristics of a ZnO buffer layer covered with a phenothiazine-based, π-conjugated donor-acceptor (D-π-A)-type organic dye (called "d-ZnO"). The use of this system for the performance enhancement of inverted bulk heterojunction polymer solar cells (PSCs) with the configuration of indium tin oxide/d-ZnO/polymer:PC71 BM/MoO3 /Ag (PC71 BM=[6,6]-phenyl C71 butyric acid methyl ester) is investigated. The layer of organic dyes anchored on the ZnO surface through carboxylate bonding reduces the shunt path on bare ZnO surface and provides better interfacial contacts and energy level alignments between the ZnO layer and the photoactive layer. This phenomenon consequently leads to highly enhanced photovoltaic parameters (fill factor, open-circuit voltage, and short-circuit current density) and power conversion efficiencies (PCEs). Inverted solar cells containing the d-ZnO layer not only revealed about 34% (PCE: 4.37%) and 18% (PCE: 7.11%) improvement in the PCEs of the representative poly-3(hexylthiophene) (P3HT) and low-band-gap poly{[4,8-bis-(2-ethyl-hexyl-thiophene-5-yl)-benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]-alt-[2-(2'-ethylhexanoyl)-thieno[3,4-b]thiophen-4,6-diyl]} (PBDTTT-C-T) polymer systems, respectively, but also showed 2-4 times longer device lifetimes than their counterparts without the organic dye layer. These results demonstrate that this simple approach used in inverted PSCs with a metal oxide buffer layer could become a promising procedure to fabricate highly efficient and stable PSCs.

High-Efficiency Indoor Organic Photovoltaics with a Band-Aligned Interlayer

“…We speculate that the serious trap-assisted recombination in PFN-based devices probably comes from the interface between the BHJ and the ETL or between the ETL and the electrode due to the high HOMO of PFN that cannot effectively block the hole, leading to e-h recombination. 63,[70][71][72] Therefore, the lower HOMO level of FTTB-PDI4 suffer from more trap-assisted recombination than Y6-O. These results are also consistent with the PV performance and dark current density results.…”

Modification of the SnO2 Electron Transporting Layer by Using Perylene Diimide Derivative for Efficient Organic Solar Cells

“…Several efforts of surface modification for metal oxide ETLs have been made using various materials, including aluminum (Lin et al, 2016), graphene (Gollu et al, 2016), quantum dot (Zeng et al, 2017), conjugated polyelectrolyte (Kim et al, 2015), and organic small molecule (Song et al, 2013). Among them, perylene diimide (PDI) derivatives, a group of organic small molecule material, have recently drawn lots of research interest due to their excellent stability and the ability to facilitate charge carrier transport by tuning the work function between the active layer and electrodes (Ling et al, 2007;Zhang et al, 2014;Wang et al, 2017).…”

Self‐assembled Poly(4‐vinylpyridine) As an Interfacial Layer for Polymer Solar Cells

“…By the insertion of the thin film of these materials between the cathode interfaces, the efficiency of the device is improved relative to that of the devices lacking these materials. The J sc of the devices is mainly enhanced by the reduction of a Schottky barrier at the interface by the formation of favorable interface dipole, leading to improve the performances of either conventional or inverted type PSCs (cPSC or iPSC) …”