Energy Transfer to a Stable Donor Suppresses Degradation in Organic Solar Cells

Abstract

Despite many advances toward improving the stability of organic photovoltaic devices, environmental degradation under ambient conditions remains a challenging obstacle for future application. Particularly conventional systems employing fullerene derivatives are prone to oxidize under illumination, limiting their applicability. Here, the environmental stability of the small molecule donor DRCN5T together with the fullerene acceptor PC 70 BM is reported. It is found that this system exhibits exceptional device stability, mainly due to almost constant short-circuit current. By employing ultrafast femtosecond transient absorption spectroscopy, this remarkable stability is attributed to two separate mechanisms: 1) DRCN5T exhibits high intrinsic resistance toward external factors, showing no signs of deterioration.2) The highly sensitive PC 70 BM is stabilized against degradation by the presence of DRCN5T through ultrafast, long-range energy transfer to the donor, rapidly quenching the fullerene excited states which are otherwise precursors for chemical oxidation. It is proposed that this photoprotective mechanism be utilized to improve the device stability of other systems, including nonfullerene acceptors and ternary blends.

Triplet‐Charge Annihilation in a Small Molecule Donor: Acceptor Blend as a Major Loss Mechanism in Organic Photovoltaics

“…Additional evidence for the assignment of the 1100 nm µs-TA band to triplets is a comparison to a previously published dicyanovinyl quinquethiophene, [66] which exhibited a strong triplet absorption at 1025 nm flanked by two polaron transitions: exactly the spectral pattern we observe for DRCN5T:PC70BM. Interestingly, previous spectroscopic work on DRCN5T:PC70BM [43,67] did not uncover the pronounced triplet formation we observe, and this highlights the value of doing TAS on long (µs) timescales and employing oxygen quenching experiments.…”

“…[41,42] It is also able to increase PC70BM air and light stability, showing negligible short-circuit current loss. [43] Of particular interest for us is the large morphological changes that are induced upon thermal annealing of DRCN5T, [32,42,44] and the motivation for this work is to investigate how such drastic changes influence the interplay between charge carriers and triplets. Intriguingly, TAS results show that thermal annealing of DRCN5T:PC70BM blends suppress charge carrier formation, despite the known ability of annealing to enhance device efficiencies in this material.…”

Improving Photovoltaic Performance of Non‐Fullerene Polymer Solar Cells Enables by Fine‐Tuning Blend Microstructure via Binary Solvent Mixtures

“…Thus, we applied the detailed photocurrent density ( J ph )‐effective voltage ( V eff ) curve measurements to gather insights into the relation between the above‐mentioned microstructures and their effects on charge dissociation probability ( P E,T ) in relevant devices. The trend of the J ph , obtained as the difference between the current under one sun illumination and that flowing in the dark, is plotted in Figure 5B versus the V eff ( V eff = V 0 − V , [ 61 ] V 0 is the compensation voltage at which J ph is zero, and V is the externally applied voltage) for the devices with different solvent blends. As exhibited in Figure 5B and Table 2, the saturated photocurrent ( J sat ) values at V eff = 2 V are 17.88, 23.33, and 24.33 mA cm −2 for CB, CF, and CF:CB co‐solvent processed devices, respectively.…”

Suppressing Kinetic Aggregation of Non‐Fullerene Acceptor via Versatile Alloy States Enables High‐Efficiency and Stable Ternary Polymer Solar Cells

“…However, binary PM6:BTP‐4Cl film shows the faster kinetic decay on a few picosecond time scale, which reflects the efficient quenching of singlet excitons in PM6 donor created by the formation of more defect states. Furthermore, the similar dynamics on the temporal scale of tens of picoseconds to nanoseconds manifest that the generated defect states have created the long‐lived, trapped charge species in binary film, [ 76 ] since they will lead to the serious charge recombination with the faster decay trend theoretically. Therefore, the introduction of the alloy states can yield the more stable fibrillar network structure of polymer donor to enhance the storage stability of ternary OSCs.…”