Significant Effect of Fluorination on Simultaneously Improving Work Function and Transparency of Anode Interlayer for Organic Solar Cells

Abstract

cathode interlayer materials that are successfully used in the efficient OSCs, anode interlayer (AIL) materials with satisfactory performances are rather rare. [15][16][17] Although several materials such as poly (3,4-ethylenedioxythiophene):(styrene sulfonate) (PEDOT:PSS) and metal oxides have been widely used as AILs, the acidic nature of PEDOT:PSS and the energy-consuming preparation process of metal oxides limit their practical uses in OSCs. [18][19][20][21] At present, the lack of ideal AILs has seriously impeded the pace toward practical application of OSCs.Currently, the enhancement of work function (WF) is the most critical issue for the development of AILs. [22,23] Many research results indicated that WFs have significant influence on the open-circuit voltage (V oc ) of the devices. [24,25] For instance, Vasilopoulou et al. enhanced the WF of molybdenum oxide AILs from 5.4 to 5.9 eV by controlling the hydrogenation degree of Mo element, by which the V oc of the device increased from 0.59 to 0.65 V. [26] Moreover, Irwin et al. prepared a NiO x AIL with a high WF of 5.4 eV, and achieved a V oc increment of 14 mV for the device. [27] However, in recent years, with the situation that the highest occupied molecular orbital (HOMO) levels of donors in fullerenefree devices are constantly downshifted for achieving high V oc , [28,29] most previously developed AILs cannot satisfy the new demands for modifying efficient OSCs because the low WFs of these materials give rise to large energy offsets with donors, which causes interfacial barrier for hole collection and leads to serious V oc loss. [30] Thus, it is particularly urgent to explore new approaches that can further enhance the WF of AILs.Among various materials, conjugated polyelectrolytes (CPEs) are promising candidates as AIL materials due to their neutral pH, excellent charge transporting capacity, and good filmforming property. [31,32] Unlike PEDOT:PSS and metal oxides, the chemical structure of CPEs can be readily modified through synthetic chemistry, which provides great opportunities for improving the WF of AILs. For example, Lee et al. enhanced the WF of p-PFP-X from 4.97 to 5.26 eV by tuning electric dipoles of the cation-anion pairs on the side chains of CPEs, and obtained an increased PCE of 9.2% in the OSC device. [33] However, these methods merely achieved limited WF enhancement and most of the developed AILs only worked well in fullerene-based OSCs. [34] Moreover, protonic acid doping has Since the highest occupied molecular orbital (HOMO) level of donors in organic solar cells (OSCs) is being constantly downshifted for achieving high open-circuit voltage (V oc ), a further enhancement of the anode work function (WF) is required. Herein, an effective approach of fluorinationis demonstrated to simultaneously improve the WF and transparency for anode interlayer (AIL) material. By fluorination, in combination with the dialysis treatment in LiCl solution, the WF of PCP-2F-Li could be significantly enhanced from 4.86 to 5.0 eV, as compared to PCP-Na...

Recent Progress and Challenges toward Highly Stable Nonfullerene Acceptor‐Based Organic Solar Cells

“…As an extension of their research, using PCP‐2F‐Li and PBDB‐TF:IT‐4F as pH‐neutral HTL and photoactive layer, respectively, highly efficient OSCs were demonstrated in both small and large‐area (1 cm 2 ), yielding 12.7% and 10.6%, respectively. [ 99 ] To achieve high efficiency in OSCs with p‐type CPE‐based HTL, synthetic strategies for the preparation of doped‐polyelectrolytes with deeper HOMO levels and concurrently high hole transport capability were found to be important.…”

Significantly Enhanced Visible‐Light H2 Evolution of Polyfluorene Polyelectrolyte by Anionic Polyelectrolyte Doping

“…Meanwhile, PCP-2F-Li possesses excellent charge transporting capacity, high conductivity and very weak fluorescence, which is highly desirable for photocatalysis. [29] Figure 1a shows the UV-vis absorption and photoluminescence (PL) spectra of PFN-Br in CH 3 OH and PCP-2F-Li in water. PFN-Br exhibits an absorption peak at 392 nm attributed to the 𝜋-𝜋* transition of the polymer backbones and maximum emission peak at 423 nm.…”

p-Doped Conducting Polyelectrolyte as an Anode Interlayer Enables High Efficiency for 1 cm2 Printed Organic Solar Cells

“…The results are consistent with the observations in previous works. 55 The high WF over 5.0 eV of PCP-3B is crucial to the formation of Ohmic contact with active layers containing polymer donors with deep HOMO levels, which is essential to the high OSC performances.…”