Self-Assembled Monolayer Enables Hole Transport Layer-Free Organic Solar Cells with 18% Efficiency and Improved Operational Stability

Abstract

We report on bulk-heterojunction (BHJ) organic photovoltaics (OPVs) based on the self-assembled monolayer (SAM) 2PACz as a hole-selective interlayer functionalized directly onto the indium tin oxide (ITO) anode. The 2PACz is found to change the work function of ITO while simultaneously affecting the morphology of the BHJ deposited atop. Cells with PM6:N3 BHJ and ITO-2PACz anode exhibit a power conversion efficiency (PCE) of 16.6%, which is greater than that measured for bare ITO (6.45%) and ITO/PEDOT:PSS (15.94%) based devices. The enhanced performance is attributed to lower contact-resistance, reduced bimolecular recombination losses, and improved charge transport within the BHJ. Importantly, the ITO-2PACz-based OPVs show dramatically improved operational stability when compared with PEDOT:PSS-based cells. When the ITO-2PACz anode is combined with the ternary PM6:BTP-eC9:PC 71 BM BHJ, the resulting cells exhibit a maximum PCE of 18.03%, highlighting the potential of engineered SAMs for use in hole-selective contacts in high-performance OPVs.

Progress in Semitransparent Organic Solar Cells

“…[ 1,2 ] PCEs of over 18% have been reported for OSCs. [ 3–8 ] In addition to the PCE enhancement, numerous studies also focused on the stability improvement of OSCs. [ 9 ] Rationally designed encapsulations can prevent OSCs from degradation induced by air and moisture and help OSCs achieving long‐term stability.…”

The Influence of Photo‐Induced Space Charge and Energetic Disorder on the Indoor and Outdoor Performance of Organic Solar Cells

“…While efficiencies are still trailing behind those of classical inorganic solar cells, [ 1–3 ] organic photovoltaics has made substantial improvements in power‐conversion efficiency in recent years. [ 4–8 ] This development was mostly fueled by the use of novel, small‐molecule acceptor materials that replaced the previously used fullerene‐based acceptors and led to improved absorption and reduced nonradiative recombination losses. [ 9–15 ] Despite the substantial amount of structural and conformational disorder present in these molecular semiconductor blends, [ 16–18 ] efficiencies of organic solar cells under standardized test conditions have been improved to >18%, [ 7,8 ] that is, substantially higher than that of highly disordered inorganic solar cells such as those based on amorphous Si absorber layers.…”

“…Reducing shunt formation during roll‐to‐roll printing over larger areas requires the use of substantially thicker active layers as is common in scientific laboratory environments. [ 25–29 ] A typical target thickness for industrial processing is around 300 nm and more [ 25,30 ] with most scientific publications focusing on active‐layer thickness of ≈100 nm [ 7,8,31–33 ] while only few reports exist of highly efficient organic solar cells with absorber thicknesses > 300 nm. [ 28,34–38 ] A key challenge for achieving high efficiencies at thicknesses around 300 nm is the efficient collection of photogenerated charge carriers which can be hindered by recombination losses caused by fairly low mobilities and non‐ideal electric field distributions caused by space‐charge effects.…”

Techniques to Facilitate 3D Analysis of Self‐Organized Nanostructure Mechanism in Polymer/Fullerene Bulk Heterojunction Device

“…[ 5–9 ] Progress to date suggests that the narrow band gap polymers with appropriate donor/acceptor interfaces could facilitate centers for fast charge transfer leading to the power conversion efficiencies in excess of 16.7%. [ 10–12 ] While there exists a good body of information relating to fullerene/polymer composition ratios, [ 13–15 ] pre/post fabrication processes techniques, [ 16–18 ] choice of solvent, and additives [ 19–21 ] comparatively less attention has been made to the nanostructure formation of these materials. [ 22–24 ] Specifically, as these materials are solution processed, the domain size, crystallinity, and donor/acceptor interfaces are much more dependent on the fabrication process as well as its composition ratios.…”