RESUMEN
The nanoscale fibrillar morphology, featuring long-range structural order, provides abundant interfaces for efficient exciton dissociation and high-quality pathways for effective charge transport, is a promising morphology for high performance organic solar cells. Here, we synthesize a thiophene terminated non-fullerene acceptor, L8-ThCl, to induce the fibrillization of both polymer donor and host acceptor, that surpasses the 20% efficiency milestone of organic solar cells. After adding L8-ThCl, the original weak and less continuous nanofibrils of polymer donors, i.e. PM6 or D18, are well enlarged and refined, whilst the host acceptor L8-BO also assembles into nanofibrils with enhanced structural order. By adapting the layer-by-layer deposition method, the enhanced structural order can be retained to significantly boost the power conversion efficiency, with specific values of 19.4% and 20.1% for the PM6:L8-ThCl/L8-BO:L8-ThCl and D18:L8-ThCl/L8-BO:L8-ThCl devices, with the latter being certified 20.0%, which is the highest certified efficiency reported so far for single-junction organic solar cells.
RESUMEN
Organic photovoltaics (OPVs) suffer from a trade-off between efficient charge transport and suppressed nonradiative recombination due to the aggregation-induced luminance quenching of organic semiconductors. To resolve this grand challenge, a π-extended nonfullerene acceptor (NFA) B6Cl with large voids among the honeycomb network is designed and introduced into photovoltaic systems. We find that the presence of a small amount of (i.e., 0.5 or 1 wt %) B6Cl can compress the molecular packing of the host acceptor L8-BO, leading to shortened π-π stacking distance from 3.59 to 3.50 Å (that will improve charge transport) together with ordered alkyl chain packing (that will inhibit nonradiative energy loss due to the suppressed C-C and C-H bonds vibrations), as validated by high-energy X-ray scattering measurements. This morphology transformation ultimately results in simultaneously improved JSC, FF, and VOC of OPVs. As a result, the maximum PCEs of PM6:L8-BO and D18:L8-BO are increased from 19.1 and 19.3% to 19.8 and 20.2%, respectively, which are among the highest values for single-junction OPVs. The university of B6Cl to increase the performance of OPVs is further evidenced in a range of polymer:NFA OPVs.
RESUMEN
Interlayer engineering is crucial for achieving efficient and stable organic solar cells (OSCs). Herein, by introducing a commercialized brominated quaternary ammonium salt, hexamethonium bromide (HB), into a perylene diimide (PDI)-structured electron transport layer (ETL), a PDINN:HB hybrid ETL with enhanced charge collection ability and environmental/operational stability is realized. Molecular dynamics simulations and Kelvin probe force microscopy indicate that strong polar bromine and amine groups can form extra interfacial dipoles in the hybrid interlayer, while X-ray photoelectron spectroscopy and electron paramagnetic resonance suggest the hybrid ETL can interact with the Ag cathode, thereby regulating the energy level arrangement at the interface. As for the results, the PDINN:HB hybrid ETL enables improved power conversion efficiency (PCE) from 17.8 to 18.4% and 18.8 to 19.4% in PM6:C5-16 bulk heterojunction- and PM6/L8-BO pseudobulk heterojunction-based OSCs, respectively. The versatility of this method is further verified by introducing a range of brominated quaternary ammonium salts into PDINN, in which a superior PCE and stability are all obtained compared to the reference device.
RESUMEN
Polymeric semiconducting materials struggle to achieve fast charge mobility due to low structural order. In this work, five 1H-indene-1,3(2H)dione-benzene structured halogenated solid additives namely INB-5F, INB-3F, INB-1F, INB-1Cl, and INB-1Br with gradually varied electrostatic potential are designed and utilized to regulate the structural order of polymer donor PM6. Molecular dynamics simulations demonstrate that although the dione unit of these additives tends to adsorb on the backbone of PM6, the reduced electrostatic potential of the halogen-substituted benzene can shift the benzene interacting site from alkyl side chains to the conjugated backbone of PM6, not only leading to enhanced π-π stacking in out-of-plane but also arising new π-π stacking in in-plane together with the appearance of multiple backbone stacking in out-of-plane, consequent to the co-existence of face-on and edge-on molecular orientations. This molecular packing transformation further translates to enhanced charge transport and suppressed carrier recombination in their photovoltaics, with a maximum power conversion efficiency of 19.4% received in PM6/L8-BO layer-by-layer deposited organic solar cells.
RESUMEN
Conjugated polymers are generally featured with low structural order due to their aromatic and irregular structural units, which limits their light absorption and charge mobility in organic solar cells. In this work, we report a conjugated molecule INMB-F that can act as a molecular bridge via electrostatic force to enhance the intermolecular stacking of BDT-based polymer donors toward efficient and stable organic solar cells. Molecular dynamics simulations and synchrotron X-ray measurements reveal that the electronegative INMB-F adsorb on the electropositive main chain of polymer donors to increase the donor-donor interactions, leading to enhanced structural order with shortened π-π stacking distance and consequently enhanced charge transport ability. Casting the non-fullerene acceptor layer on top of the INMB-F modified donor layer to fabricate solar cells via layer-by-layer deposition evidences significant power conversion efficiency boosts in a range of photovoltaic systems. A power conversion efficiency of 19.4% (certified 18.96%) is realized in PM6/L8-BO binary devices, which is one of the highest reported efficiencies of this material system. The enhanced structural order of polymer donors by INMB-F also leads to a six-fold enhancement of the operational stability of PM6/L8-BO organic solar cells.
RESUMEN
Organic semiconductors are generally featured with low structure order in solid-state films, which leads to low charge-transport mobility and strong charge recombination in their photovoltaic devices. In this work, a "polycrystal-induced aggregation" strategy orders the polymer donor (PM6) and non-fullerene acceptor (L8-BO) molecules during solution casting with the assistance of PM6 polycrystals that are incubated through a vapor diffusion method, toward improved solar cell efficiency with either thin or thick photoactive layers. These PM6 polycrystals are redissolved in chloroform to prepare PM6 pre-aggregates (PM6-PA), and further incorporated into the conventional PM6:L8-BO blend solutions, which is found to prolong the molecular organization process and enhance the aggregation of both the PM6 and the L8-BO components. As the results, with the assistance of 10% PM6-PA, PM6:L8-BO solar cell devices obtain power conversion efficiencies (PCEs) from 18.0% and 16.2% to 19.3% and 17.2% with a 100 nm-thick and 300 nm-thick photoactive layer, respectively.