Ultrafast Hole Transfer and Carrier Transport Controlled by Nanoscale-Phase Morphology in Nonfullerene Organic Solar Cells

Abstract

Nonfullerene acceptors (NFAs) have attracted great attention in high-efficiency organic solar cells (OSCs). While the effect of molecular properties including structures and energetics on charge transfer has been extensively investigated, the effect of macroscopic-phase properties is yet to be revealed. Here we have performed a correlation study of the nanoscale-phase morphology on the photoexcited hole transfer (HT) process and photovoltaic performance by combining ultrafast spectroscopy with high temporal resolution and photo-induced force microscopy (PiFM) with high spatial and chemical resolution. In PM6/IT-4F, we observe biphasic HT behavior with a minor ultrafast (<100 fs) interfacial process and a major diffusion-mediated HT process until ∼100 ps, which depends strongly on phase segregation. Because of the interplay between charge transfer and transport, a compromised domain size of 20–30 nm for NFAs shows the best performance. This study highlights the critical role of phase morphology in high-efficiency OSCs.

Simple Non‐Fused Electron Acceptors Leading to Efficient Organic Photovoltaics

“…Here,t he kinetics of 528 nm, 543 nm, and 549 nm were chosen to represent the hole transfer process of PBDB-TF:PTIC,P BDB-TF:PTB4F,a nd PBDB-TF:PTB4Cl, respectively,w ith negligible contamination from acceptor materials.T he hole transfer kinetics in blend films (Figure 4d)c an be fitted by ab iexponential function: i = A 1 exp(Àt/t 1 ) + A 2 exp(Àt/t 2 ), with fast and slow component lifetimes of t 1 and t 2 and prefactors of A 1 and A 2 . As shown by previous studies, [18] the fast component can be ascribed to the direct interfacial hole transfer process and the slow component to the diffusion of excitons toward interfaces before dissociation. All three blends show similarly ultrafast rising kinetics,w ith al ife-time of 0.21 ps,0 .22 ps,a nd 0.18 ps corresponding to the interfacial hole transfer process,aswell as as low process of 6.14 ps,1 3.37 ps,a nd 14.56 ps corre- sponding to the diffusion-mediated hole transfer process for PTIC-, PTB4F-, and PTB4Cl-based blend films,respectively (Table S3).…”

High‐Performance All‐Polymer Solar Cells with a Pseudo‐Bilayer Configuration Enabled by a Stepwise Optimization Strategy

“…Of note is that HT process consists of an ultrafast hole transfer process at the interface, as characterized by τ 1 , as well as a diffusion mediated process controlled by D/A domain size and aggregation strongly, as characterized by τ 2 . [ 37,38 ] As shown in Table S3, Supporting Information, the HT process in BHJ/LBL films show a fast component with τ 1 of ≈0.195/≈0.215 ps, and a slow component τ 2 of 7.140/7.468 ps, respectively. As a direct consequence, the proportion of diffusion mediated transfer process accounts for more in the whole HT process in the LbL film, indicating the significant role of exciton diffusion in the LbL blend microstructure.…”

Intrinsically Chemo- and Thermostable Electron Acceptors for Efficient Organic Solar Cells

“…As previous studies of domain size characteristics on the organic BHJ blends, 19,[39][40] the hole transfer process consists of an ultrafast hole-transfer process at the interface, as characterized by the fast lifetime τ1, as well as the diffusion of excitons towards interfaces before dissociation, as characterized by the slow lifetime τ1. [41][42] All of the fitting parameters are listed in Table S1. All the kinetics exhibit similar the fast rise account for ~ 40% with characteristic times (τ1) for PBDB-T:Q1-0F, PBDB-T:Q1-2F, and PBDB-T:Q1-4F of 0.119, 0.141, and 0.121 ps, respectively, indicating high hole transfer rate at the polymer donor and Q1-XF acceptor interface.…”