Reducing the Excitonic Loss at Donor/Acceptor Heterojunction with Negligible Exciton Dissociation Driving Force

Abstract

A breakthrough for non-fullerene acceptors (NFAs) is their efficient photocharge generation and low nonradiative voltage loss (ΔV nrad) in a condition of negligible energy offset (ΔG S1,CT) between the lowest singlet state (S1) and the relaxed charge transfer (CT) state. This inspires the idea of viewing the donor/acceptor (D/A) binary blend as a single component in organic solar cells (OSCs) and attracts tremendous studies on the D/A pairs with negligible ΔG S1,CT. Unfortunately, an arbitrarily chosen material combination usually results in severe photovoltaic performance loss. To solve this problem, we present a diffused heterojunction (DHJ) doping strategy at the D/A heterojunction with small ΔG S1,CT. The electronic doping alleviates the performance loss by accelerating the exciton dissociation rate and reducing the ΔV nrad. After examining the DHJ doping strategy in other six NFA material combinations, we are confident to point out that our work opens an avenue for pursuing intrinsic high OSC performance comparing with other single-component photovoltaic technologies.

N-dopants optimize the utilization of spontaneously formed photocharges in organic solar cells

“…The corresponding p-p distances of 3.56 Å and 3.55 Å with similar coherence lengths of 2.85 nm and 2.83 nm, demonstrate little influence of N-DMBI on the morphology of the dilute film. The coexistence of Routes 1 and 2 in the dilute BHJ film was confirmed from the temperature-dependent photoluminescence (PL) spectrum measurement, 14,30,31 since CS in the neat Y6 domain and PM6/Y6 heterojunction shows distinct intensity-varying trends when cooling from room temperature (Fig. S3, ESI †).…”

Solid Solvation Assisted Electrical Doping Conserves High‐Performance in 500 nm Active Layer Organic Solar Cells

“…[ 45 ] The phenomena that the electrical doping facilitates heterojunction photocharge generation have been reported in bilayer devices according to our previous studies. [ 13,14,19 ] Herein, we demonstrate that this advantage can be successfully applied in high‐efficiency BHJ device by correcting the dopant's componential location.…”

“…Theoretically, the electrical doping can facilitate exciton splitting at the donor/acceptor heterojunction and in neat non-fullerene acceptor (NFA) by tuning the energy landscape. [13][14][15][16] The doping induced charge density increment may also modify the charge carrier profile within BHJ film and the corresponding internal electric field. [17][18][19] Though the electrical doping seems like a rational solution to the problems in thick film OSCs, the unexpected useless function on PCE improvement hinders its practical application.…”

Identifying and Amplifying the Spontaneously Formed Photo‐Charge Contribution in Opaque and Semitransparent Organic Photovoltaics

“…Since it is challenging to obtain the accurate SP yield in each sample, we alternatively deduce the SP yield by the energy barrier height (E a ) of SP→LE transition from temperature-dependent PL measurements (Figures S1 and S2, Supporting Information). [7,19,31,32] In a three-state equilibrium between LE, triplet state (T 1 ), and SP (Figure S1, Supporting Information), the T 1 →SP transition is spin-forbidden [33] and the energy offset between T 1 and LE (0.684 eV for N4, 0.538 eV for L8-BO, and 0.527 eV for BTP-eC9) is too large to be overcome by thermal energy (Figure S2, Supporting Information). The variation of PL intensity is mostly related to the SP→LE transition.…”