19.31% binary organic solar cell and low non-radiative recombination enabled by non-monotonic intermediate state transition

Abstract

Non-fullerene acceptors based organic solar cells represent the frontier of the field, owing to both the materials and morphology manipulation innovations. Non-radiative recombination loss suppression and performance boosting are in the center of organic solar cell research. Here, we developed a non-monotonic intermediate state manipulation strategy for state-of-the-art organic solar cells by employing 1,3,5-trichlorobenzene as crystallization regulator, which optimizes the film crystallization process, regulates the self-organization of bulk-heterojunction in a non-monotonic manner, i.e., first enhancing and then relaxing the molecular aggregation. As a result, the excessive aggregation of non-fullerene acceptors is avoided and we have achieved efficient organic solar cells with reduced non-radiative recombination loss. In PM6:BTP-eC9 organic solar cell, our strategy successfully offers a record binary organic solar cell efficiency of 19.31% (18.93% certified) with very low non-radiative recombination loss of 0.190 eV. And lower non-radiative recombination loss of 0.168 eV is further achieved in PM1:BTP-eC9 organic solar cell (19.10% efficiency), giving great promise to future organic solar cell research.

Understanding and Suppressing Non‐Radiative Recombination Losses in Non‐Fullerene Organic Solar Cells

“…The heterogeneity of local morphologies in bulk‐heterojunctions in terms of D‐A blend ratio, different molecular weight polymers, additives, growth, and annealing conditions strongly influences the energy levels and dynamics of interfacial CT states, [ 54,100 ] and thus voltage losses in general. An often observed trend is that a more aggregated morphology leads to relatively larger non‐radiative losses, [ 9,24,101,102 ] which could be ascribed to reduced fluorescence emission efficiency [ 103 ] and/or increased the local D‐A HOMO offset in the aggregated solid state. [ 104 ] Preventing aggregation of NFAs by dispersing them into a polymer: fullerene matrix has been shown to reduce Δ V oc,nr .…”

“…[ 8,12–14 ] An additional and significant advantage in the optimization of the photovoltaic properties of donor: NFA blends are their relatively straightforward adjustment of the frontier energy levels and optical gaps over a wide energy range, by engineering acceptor–donor–acceptor (A–D–A) or A–DA'D–A‐type (such as Y6) fused groups in their molecular backbones. [ 15–18 ] This has brought the power conversion efficiency ( PCE ) of the state‐of‐the‐art NFA OSCs to over 19% in a single‐junction [ 19–25 ] and 20% in a two‐terminal tandem configuration, [ 26,27 ] respectively.…”

Nonradiative Energy Loss Generated by Two Hidden Trade-Offs in Non-Fullerene Organic Solar Cells with the Positive Correlation between JSC and VOC

“…6 However, the PCE (∼16%) obtained by the molecular modification strategy achieving positive correlation is not satisfactory 7 and is far below the current record PCE of ∼20%. 8,9 This shows that the simultaneous increases of J SC and V OC can improve efficiency but has not resulted in significant breakthroughs of PCE.…”

Detrimental Effects of “Universal” Singlet Photocrosslinkers in Organic Photovoltaics

“…The power conversion efficiency (PCE) of organic photovoltaics (OPVs) has been dramatically improved to over 19% in the past few decades. − This is mainly due to the development of new organic semiconductors, including non-fullerene electron acceptors, which are suitable for photoinduced charge generation and charge transport. − The high performance is achieved by mixed bulk heterojunction (BHJ) films, in which the donor and acceptor molecules form interconnected material networks with a large interfacial area. The mixed morphology in the BHJ film has a large effect on the OPV performance and is sensitive to the film preparation and processing conditions; therefore, the OPV stability may depend on the morphology stability. , This effect is particularly pronounced in polymer/fullerene systems, where the long-term thermal annealing of the films results in extensive aggregation of the fullerene acceptors .…”