Mechanistic Investigation into Dynamic Function of Third Component Incorporated in Ternary Near‐Infrared Nonfullerene Organic Solar Cells

Abstract

Organic solar cells (OSCs) consisting of an ultralow‐bandgap nonfullerene acceptor (NFA) with an optical absorption edge that extends to the near‐infrared (NIR) region are of vital interest to semitransparent and tandem devices. However, huge energy‐loss related to inefficient charge dissociation hinders their further development. The critical issues of charge separation as exemplified in NIR‐NFA OSCs based on the paradigm blend of PTB7–Th donor (D) and IEICO–4F acceptor (A) are revealed here. These studies corroborate efficient charge transfer between D and A, accompanied by geminate recombination of photo‐excited charge carriers. Two key factors restricting charge separation are unveiled as the connection discontinuity of individual phases in the blend and long‐lived interfacial charge‐transfer states (CTS). By incorporation of a third‐component of benchmark ITIC or PC71BM with various molar ratios, these two issues are well‐resolved accordingly, yet in distinctly influencing mechanisms. ITIC molecules modulate film morphology to create more continuous paths for charge transportation, whereas PC71BM diminishes CTS and enhances electron transfer at the D/A interfaces. Consequently, the optimal untreated ternary OSCs comprising 0.3 wt% ITIC and 0.1 wt% PC71BM in the blend deliver higher JSC values of 21.9 and 25.4 mA cm‐2, and hence increased PCE of 10.2% and 10.6%, respectively.

Unraveling the Mystery of Ternary Organic Solar Cells: A Review on the Influence of Third Component on Structure–Morphology–Performance Relationships

“…This decrease in V oc , which is affected by higher dielectric effects in binary configuration, has been experimentally proven in earlier work by Veldman et al [ 170 ] In ternary configurations with enhanced dielectric screening, we mostly see a constant V oc , which deemed the V oc unaffected by the dielectric screening. [ 114,145,147 ] Interestingly, in another article by Duan et al, [ 172 ] they observed an increase in V oc at the optimum ternary ratio when the dielectric screening effects took place. This could be due to the improved CT and CS coupling which promotes enhanced k CT→CS and results in lower nonradiative recombination loss to V oc .…”

“…Most reports showed significant improvement in J sc and FF with enhanced k CT→CS due to the dielectric screening effect. [ 114,145,146,167,169 ] This is quite intuitive considering a better dissociation of charges leads to improved charge mobility and transport. However, as in Equation (), any form of decrease in Δ E CT‐G increases k nr , which is detrimental toward V oc .…”

Suppressing Kinetic Aggregation of Non‐Fullerene Acceptor via Versatile Alloy States Enables High‐Efficiency and Stable Ternary Polymer Solar Cells

“…The dynamics of these TA spectra display two interesting phenomenon: one is that the kinetic decay processes of two ternary blends are faster than that of binary system in the shorter timescale part (<1 ps), which reflects chiefly the hole injection information and can be in good consistence with the results of transient GSB features. [ 53 ] The other is that these TA decays of two ternary blends (especially for the PM6:DRCN5T:BTP‐4Cl film) at the longer temporal delay as seen from 100 ps to 7 ns are slower than the kinetics of binary PM6:BTP‐4Cl film, basically referring to the nature of non‐geminate recombination. [ 54 ] The prolonged lifetime of CS species is in favor of the extraction and collection of the photogenerated charge carriers to promote electricity generation, coinciding well with the higher FFs and more efficient EQE response observed in ternary OSCs.…”

Developing Halogen‐Free Polymer Donors for Efficient Nonfullerene Organic Solar Cells by Addition of Highly Electron‐Deficient Diketopyrrolopyrrole Unit

“…Our previous work has established that a fullerene derivative acceptor would largely enhance electron extraction and reduce charge recombination. [ 48,49 ] Inspired by it, we next used PC 71 BM as a third component in the P75:Y6 binary blend with a P75:Y6:PC 71 BM ratio of 1.5:1.4:0.1, 1.5:1.3:0.2, and 1.5:1.2:0.3 wt% in ternary blends, which are denoted as T 0.1 , T 0.2 , and T 0.3 with respect to PC 71 BM wt%, respectively, for simplicity in the following discussion. The optical absorptions of binary and ternary blend films in comparison with their neat films are shown in Figure 1c.…”