Reducing Limitations of Aggregation‐Induced Photocarrier Trapping for Photovoltaic Stability via Tailoring Intermolecular Electron–Phonon Coupling in Highly Efficient Quaternary Polymer Solar Cells

Abstract

The kinetic aggregation of nonfullerene acceptors under nonequilibrium conditions can induce electron–phonon interaction roll‐off and electronic band structure transition, which represents an important limitation for long‐term operational stability of organic solar cells (OSCs). However, the fundamental underlying mechanisms have received limited attention. Herein, a photophysical correlation picture between intermolecular electron–phonon coupling and trapping of electronic excitation is proposed based on the different aggregation behaviors of BTP‐eC9 in bulk‐heterojunction and layer‐by‐layer processed multicomponent OSCs. Two separate factors rationalize their correlation mechanisms: 1) the local lattice and/or molecular deformation can be regarded as the results of BTP‐eC9 aggregates in binary system under continuous heating, which brings about attenuated intermolecular electron–phonon coupling with intensified photocarrier trapping. 2) The higher density of trap states with more extended tails into the bandgap give rise to the formation of highly localized trapped polarons with a longer lifetime. The stabilized intermolecular electron–phonon coupling through synergistic regulation of donor and acceptor materials effectively suppresses unfavorable photocarrier trapping, delivering the improved device efficiency of 18.10% and enhanced thermal stability in quaternary OSCs. These results provide valuable property–function insights for further boosting photovoltaic stability in view of modulating intermolecular electron–phonon coupling.

Triggering favorable energy landscape: a general approach towards highly efficient and photostable organic solar cells

“…Previously, we have proposed a photophysical correlation picture between intermolecular electron–phonon coupling and trapping of electronic excitation behind the kinetic aggregation of BTP-eC9 under thermal stress. 26 The BTP-eC9 aggregates give rise to the decreased intermolecular electron–phonon coupling and the increased density of trap states with more extended tails into the bandgap. 26 Based on the above photophysical phenomenon inspiration, we point out that the existence of an unfavorable energy landscape in the actual OPV devices might induce the deterioration of photovoltaic performance under continuous sunlight illumination according to the following factors.…”

“…26 The BTP-eC9 aggregates give rise to the decreased intermolecular electron–phonon coupling and the increased density of trap states with more extended tails into the bandgap. 26 Based on the above photophysical phenomenon inspiration, we point out that the existence of an unfavorable energy landscape in the actual OPV devices might induce the deterioration of photovoltaic performance under continuous sunlight illumination according to the following factors. First, the high degree of energetic disorder associated with the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) energy levels widens the distribution of electronic states, thus creating a large number of band tail states.…”

Toward high-performance organic photovoltaics: the new cooperation of sequential solution-processing and promising non-fullerene acceptors

“…To overcome the limitations of D/A binary systems, ternary components systems were developed. 54–56 In recent years, several groups 57–60 have tried to combine sequential solution-processing and ternary components systems. In 2018, Yang et al 61 fabricated a ternary OPV with a controlled structure by sequential solution-processing.…”

Green‐Solvent‐Processed 17% Efficient Polymer Solar Cell Achieved Synergistically by Aligning Energy Levels and Improving Morphology with the Quaternary Strategy

“…[ 55–57 ] To address the issue that simultaneously increased V OC and J SC were difficult to be achieved by following either the “voltage‐increased” or the “current‐increased” ternary approach, the quaternary approach has been reported. [ 58–63 ] Due to the use of one more component involved in the active layer, the quaternary strategy allows us to combine two extra components together to synergistically modulate the complicated photon‐to‐electron conversion mechanisms that are involved in photovoltaic cells. Recently, Yan et al selected PTQ10 and PC 71 BM as the guest components and PM6:N3 as the host binary system to fabricate a high‐efficiency quaternary device with a PCE of 17.73%.…”