Reduced Nonradiative Energy Loss Caused by Aggregation of Nonfullerene Acceptor in Organic Solar Cells

Abstract

current. The latter is the value of qV OC a solar cell with that bandgap would have at a temperature of 300 K illuminated by 1 sun unconcentrated illumination and assuming emission of luminescence into the 2π halfspace above the solar cell. [16][17][18][19] 2) qV OC SQ − qV OC rad (ΔE 2 ) is the loss due to the absorption edge being nonabrupt and therefore primarily due to radiative recombination below the bandgap. [20][21][22][23][24] 3) The third loss is due to nonradiative recombination (ΔE 3 ). As the first term ΔE 1 is unavoidable for any solar cell, the main opportunities for reducing E loss to improve the V OC lie in the other two terms.The second term, ΔE 2 , can be reduced by elevating the charge transfer (CT) state. For instance, it has been demonstrated that when the ionic potential (IP) and electronic affinity (EA) of a donor are nearly aligned with those of an acceptor, the energetic offset from E g to E CT can be very small, resulting in a negligible ΔE 2 . [20,21,25,26] In contrast, when the IP and EA of a donor are much larger than those of an acceptor, as observed in many OSCs based on polymer donors and fullerene acceptors, ΔE 2 can be as large as over 0.60 eV. [17,27,28] The third term, ΔE 3 , can be varied from 0.25 to 0.48 eV. [29][30][31][32][33][34][35] As is known, for an OSC under open-circuit condition, an electron-hole pair at the CT state transits to the ground state by either radiative recombination or nonradiative recombination, so the electroluminescence (EL) emission can be used as a tool to monitor the nonradiative recombination. [21,28,[31][32][33] There have been many studies to investigate ΔE 3 for OSCs based on various photoactive materials. [28,30,36] For instance, for an OSC based on the polymer donor P3TEA and acceptor SF-PDI2, the electroluminescence quantum efficiency (EQE EL ) was as high as 5 × 10 −5 , corresponding to a ΔE 3 of 0.26 eV, [20] while for OSCs based on polymer donors and fullerene acceptors, ΔE 3 can surpass 0.40 eV. [30,31] Up to date, the methodology for tuning ΔE 3 has not yet been established. Considering that ΔE 1 is unavoidable and ΔE 2 can be reduced to a negligible value, the modulation of ΔE 3 is critical in the field of OSCs.Here, we report a new method to reduce E loss in an OSC based on the polymer donor PBDB-T and nonfullerene acceptor IT-4F by incorporating a small molecular material named NRM-1 in the photoactive layer. We selected the PBDB-T:IT-4F system to conduct the study because the IP and EA of PBDB-T are much larger than those of IT-4F and the energetic offset between E g and E CT , referring to ΔE 2 , can be obviously Reducing energy loss (E loss ) is of critical importance to improving the photovoltaic performance of organic solar cells (OSCs). Although nonradiative recombination ( E loss nonrad ) is investigated in quite a few works, the method for modulating E loss nonrad is seldom reported. Here, a new method of depressing E loss is reported for nonfullerene OSCs. In addition to ternary-blend bulk heterojunction (BHJ) solar cells...

As‐Cast Ternary Organic Solar Cells Based on an Asymmetric Side‐Chains Featured Acceptor with Reduced Voltage Loss and 14.0% Efficiency

“…The expansion also accompanies the reduction of disorder (Figure b), which is evidenced by the narrowing of Urbach tails of both bulk and charge‐transfer (CT) states. The blueshift of the band edge as well as the reduced disorder are also coherent with the observed charge transport improvement in ternary blends, where the morphological evolution upon adding IDIC leads to the reduced disorder and isolated domain formation via increased crystallization of PM6 while forming an intimate mixture of acceptor domains …”

Single-Component Non-halogen Solvent-Processed High-Performance Organic Solar Cell Module with Efficiency over 14%

“…As listed in Table S9, the EQE EL value of the PM6:Y6-based devices processed from XY is an order of magnitude lower than that of CF, and the calculated DE Article non-fullerene acceptor Y6 in the XY-processed film, which led to the voltage drop of the resulting device. 44 In addition, to further test the universality of the PM6:DTY6 in other non-halogen solvents, toluene (TL) and 1,2,4-trimethyl-benzene (TMB) were selected as processing solvents to fabricated devices based on the blends of PM6:DTY6 and PM6:Y6. The J-V curves are presented in Figure S19 and the corresponding device data are summarized in Table S10.…”

Low Temperature Aggregation Transitions in N3 and Y6 Acceptors Enable Double‐Annealing Method That Yields Hierarchical Morphology and Superior Efficiency in Nonfullerene Organic Solar Cells

“…[24] The T g is also a critical parameter even during the casting of the BHJ active layer, [25,26] and can be used to qualitatively predict the stability of organic semiconductor devices. [27,28] The emergence of nonfullerene small molecule acceptors (NFAs) [8,10,19,[29][30][31][32][33][34] has enriched, yet complicated matters. The differences between NFAs in molecular geometry, stiffness, and size might have a profound effect on T g and the aggregation behavior of the NFAs, optimization protocols, and stability of the active layer.…”

“…The emergence of nonfullerene small molecule acceptors (NFAs) [ 8,10,19,29–34 ] has enriched, yet complicated matters. The differences between NFAs in molecular geometry, stiffness, and size might have a profound effect on T g and the aggregation behavior of the NFAs, optimization protocols, and stability of the active layer.…”