Exploring the Charge Dynamics and Energy Loss in Ternary Organic Solar Cells with a Fill Factor Exceeding 80%

Abstract

Ternary architecture is a promising strategy to enhance power conversion efficiencies (PCEs) of organic solar cells (OSCs). However, among all the photovoltaic parameters that govern the final PCEs, the fill factor (FF) for ternary OSCs is generally below 78%, limiting solar cells’ performance. Here, charge dynamics in the ternary cells PM6:DRTB‐T‐C4:Y6 with a FF of 80.88% and a PCE of 17.05% are thoroughly investigated by a series of transient characterization technologies, including transient absorption spectroscopy, transient photovoltage, and transient photocurrent measurements. The impressive FF results from effective exciton dissociation, enhanced charge transport and suppressed recombination in ternary cells. Moreover, the correlation between the measured FF and the charge recombination‐extraction competition is quantitatively analyzed by using a circuit model. The ternary cells also show small energy loss (Eloss). The findings here provide insight into achieving high‐FF and low‐Eloss ternary OSCs.

Enhanced Charge Transport and Broad Absorption Enabling Record 18.13% Efficiency of PM6:Y6 Based Ternary Organic Photovoltaics with a High Fill Factor Over 80%

“…The optimal ternary OSC has the smallest k nge of 1.04 × 10 −17 m 3 s −1 and has two orders of magnitude difference between k nge and k L (Figure 4d), which indicate the suppressed charge recombination and thus the improved charge transport in the ternary device. [32] We quantitatively calculate the energy loss of the ternary device as per the framework of Marcus theory (Table S7, Supporting Information). [50,51] The total energy loss (E loss ) is described as: E g − eV OC = (E g − E CT ) + ΔE rad + ΔE non − rad , [52] where E g represents the bandgap determined by the intersection of absorption and emission spectra of the films (Figure S21, Supporting Information).…”

“…Additionally, the smaller dark leakage current in region I originates from the reduced shut resistance (Figure S16, Supporting Information), also contributing to the high FF in the ternary device. [ 32 ] We further study the plots of V oc versus light intensity ( P ) to elucidate the charge recombination kinetics. The dependence of V oc on P is described as ( K B is the Boltzmann constant, T is the absolute temperature, and q is the elemental charge).…”

“…The optimal ternary OSC has the smallest k nge of 1.04 × 10 −17 m 3 s −1 and has two orders of magnitude difference between k nge and k L (Figure 4d), which indicate the suppressed charge recombination and thus the improved charge transport in the ternary device. [ 32 ]…”

“…[30] Consequently, the FF is closely associated with the charge generation, transport, and collection processes, governed by competition relationship of carrier extraction and recombination. [31,32] The PM6:Y6 is a classic BHJ system as a first OSC binary device over 15% efficiency. So far, the highest PCE of the PM6:Y6 based ternary OSC (PM6:Y6:AQ X-3 ) has been reported to be 18.01%, which mainly results from the elevated J sc and V oc , but the further improvement in PCE is hampered by the relatively low FF of 77.2%.…”

Stable dinitrile end-capped closed-shell non-quinodimethane as a donor, an acceptor and an additive for organic solar cells

“…Different from binary OSCs, ternary OSCs appear to be a viable tool to extend light absorption, facilitate exciton dissociation and optimize the morphology, leading to an improvement of photovoltaic performances. 19–27 Cascade energy alignment could be achieved by introducing a third component with suitable energy levels, which is beneficial to suppress charge recombination. 28,29 Another significant function of the third component is to improve the compatibility and miscibility with the binary blend films.…”