Non‐Radiative Recombination Energy Losses in Non‐Fullerene Organic Solar Cells

Abstract

Impressive short-circuit current density and fill factor have been achieved simultaneously in single-junction organic solar cells (OSCs) with the emergence of high-performance non-fullerene acceptors. However, the power conversion efficiencies (PCEs) of OSCs still lag behind those of inorganic and perovskite solar cells, mainly due to the modest open-circuit voltage (V OC ) imposed by relatively large energy loss (E loss ). Generally, E loss in solar cells can be divided into three parts. Among them, ΔE 1 is inevitable for all photovoltaic cells and depends on the optical bandgap of solar cells, while radiative recombination energy loss, ΔE 2 , in OSCs can approach the negligible value via finely matching donor with acceptor material in the blend. The relatively large non-radiative recombination energy loss, ΔE 3 , becomes the main barrier to further reduce E loss and thus enhance PCE in non-fullerene acceptor-based OSCs. In this review, the recent studies and achievements about ΔE 3 in non-fullerene acceptor-based OSCs have been summarized from the aspects of material design, morphology manipulation, ternary strategy, mechanism, and theoretical study. It is hoped that this review helps to get a deep understanding and boost the advance of ΔE 3 study in OSCs.

Donor–Acceptor Copolymers with Rationally Regulated Side Chain Orientation for Polymer Solar Cells Processed by Non-Halogenated Solvent

“…To 55 The JSC calculated from EQE are 24.22 and 21.29 mA cm -2 for PBTFO-T-1 and PBTFO-T-2 based devices, respectively, both of which are within a 5% error region, demonstrating the reliability of the obtained data. The higher FF of the PBTFO-T-1 based devices is presumably ascribed to its better charge transport in the active layer and less charge recombination, which will be investigated in the followed measurements.…”

“…16 % with an open-circuit voltage (V OC ) of 0.80 V, a short-circuit current density (J SC ) of 25.34 mA • cm −2 and a FF of 70.99 %. However, the optimal PBTFO-T-2-based devices can only achieve a PCE of 9.39 % with a V OC of 0.78 V, a J SC of 21.85 mA • cm −2 and a FF of 55 The J SC values calculated from EQE are 24.22 and 21.29 mA • cm −2 for PBTFO-T-1-and PBTFO-T-2-based devices, respectively, both of which are within a 5 % error region, demonstrating the reliability of the obtained data. The higher FF of the PBTFO-T-1-based devices is presumably ascribed to their better charge transport in the active layer and less charge recombination, which will be investigated later.…”

Single‐Junction Organic Solar Cells with 19.17% Efficiency Enabled by Introducing One Asymmetric Guest Acceptor

“…In comparison, the ternary device shows a higher EQE EL of 4.05 × 10 −4 , leading to a lower Δ E 3 of 0.201 eV. [ 78,79 ] This result is not only induced by the favorable ternary bulk microstructure (Figure 4) and reduced Urbach energy value (Figure S21, Supporting Information) in ternary devices, [ 80 ] the enhanced hybridization of the charge‐transfer state with the first excited state, [ 18,80 ] the suppressed vibrational coupling, the improved PLQY and exciton diffusion length of the L8‐BO:BTP‐2F2Cl alloy‐like phase. [ 31,42 ] Noted that the Δ E 3 calculated by combining EL and FTPS tests and the Exp.…”

Bulk heterojunction organic photovoltaic cells based on D–A type BODIPY small molecules as non-fullerene acceptors

“…The energy loss (E loss ) in the PSCs is an important parameter and can be expressed as E loss = E g À qV OC , where E g is estimated from the onset of the EQE spectra of the device. [67][68][69] The values of E loss for the PSCs based on CF 3 -BDP-TPA and CF 3 -BDP-Cz are about 0.52 eV and 0.47 eV, respectively. In the case of PSCs, the large HOMO and LUMO offset between the donor and acceptor is needed for exciton dissociation and subsequent charge transfer owing to the high exciton binding energy and leads to a high value of E loss .…”