Concentration dependent energy levels shifts in donor-acceptor mixtures due to intermolecular electrostatic interaction

Abstract

Recent progress in the improvement of organic solar cells lead to a power conversion efficiency to over 16%. One of the key factors for this improvement is a more favorable energy level alignment between donor and acceptor materials, which demonstrates that the properties of interfaces between donor and acceptor regions are of paramount importance. Recent investigations showed a significant dependence of the energy levels of organic semiconductors upon admixture of different materials, but its origin is presently not well understood. Here, we use multiscale simulation protocols to investigate the molecular origin of the mixing induced energy level shifts and show that electrostatic properties, in particular higher-order multipole moments and polarizability determine the strength of the effect. The findings of this study may guide future material-design efforts in order to improve device performance by systematic modification of molecular properties.

Simple approach for an electron extraction layer in an all-vacuum processed n-i-p perovskite solar cell

“…One potential explanation is, that electrostatic interaction between C 60 and BCP can cause shifts in their respective energy levels (e.g., LUMO of C 60 ), which enhances the injection/extraction property for the ITO contact. This is in line with a recent report that the energy levels of organic semiconductor molecules can be shifted in the mixed phase, including C 60 , via inter molecular electro-static interaction and structural orders [49][50][51] . the PCE is much higher (15.1%) than the PCE of 1:1 mixed film.…”

“…The similar PLQY values with the similar slope suggest that the there is no significant differences in the interface recombination for both films [52,53] . Hence, based on the datasets discussed above, it can be deduced that the improvement in the device performance using the mixed layer is more likely attributed to the energy level shift via electro-static interaction and structural orders of organic semiconductors as previously reported [49][50][51] . however, the mixed layer significantly promotes the charge extraction and leads to a PCE increase from 13% to 18%.…”

Barrier-Free Charge Separation Enabled by Electronic Polarization in High-Efficiency Non-fullerene Organic Solar Cells

“…In the case of the fullerene acceptor of PC 71 BM, the interior of the carbon ball exhibits positive ESPs, but the outer surface shows slightly negative ESPs, which is favorable for stabilization of the holes (positive S + ) and destabilization of the electrons (negative S – ) and thus brings about a relatively larger P + with respect to P – . This result is similar to that for oligoacenes and sexithiophene with marked negative ESPs on the molecular backbone surfaces. , To confirm the role of molecular ESPs in determining S ± , the positive and negative surface areas and the average positive and negative surface ESPs ( and ) have been calculated according to Politzer’s descriptors; the results are listed in Table S2. Apparently, the proportions of the positive surface area for the NF acceptors (>70%) are larger than those for the donor molecules; along with a stronger , IT-4F and Y6 are indeed more likely to stabilize electrons and destabilize holes.…”

Designing and Screening High‐Performance Non‐Fullerene Acceptors: A Theoretical Exploration of Modified Y6

“…The stronger dipole moment of an NFA would result in increasing self‐assembly and molecular packing with higher order, which is good for charge carrier diffusion. [ 28 ] However, at the donor–acceptor interface, it would hinder charge transfer due to bad mixing of donors and acceptors. Moreover, the large domain size due to strong aggregation of molecules is not beneficial for exciton diffusion.…”