Donor Derivative Incorporation: An Effective Strategy toward High Performance All‐Small‐Molecule Ternary Organic Solar Cells

Abstract

small-molecule acceptor are currently attracting enormous attentions due to their distinct advantages such as monodispersion, easy purification, and scalability with negligible batch-to-batch variation. [1][2][3][4][5] Tremendous progress has been made in the past years on rational molecule design, device engineering, and interface modification, leading to over 10% power conversion efficiencies (PCEs) in ASM OSCs with fullerene derivatives as the electron acceptor. [6][7][8][9] However, the difficulties of controlling the morphology (e.g., crystallinity and domain size) of active-layer constrained the development of ASM OSCs. [10][11][12] Furthermore, the device performance of ASM OSCs is often sensitive to the film thickness of ≈100 nm in most reports, which hinders the future high-throughput device fabrication processing like roll-to-roll and ink jet printings. [13][14][15] Thus, it is worth finding an effective method to tune the active-layer morphology, and attain high efficiency with thick active layers. Benzodithiophene terthiophene rhodanine (BTR) stands out as an excellent thickfilm OSC material with respectable (while not enough) efficiency of over 9% pairing with fullerene acceptor. Finding effective methods to further enhancing the BTR based thickfilm OSC device efficiency is expected to be an important and Thick-film all-small-molecule (ASM) organic solar cells (OSCs) are preferred for large-scale fabrication with printing techniques due to the distinct advantages of monodispersion, easy purification, and negligible batch-to-batch variation. However, ASM OSCs are typically constrained by the morphology aspect to achieve high efficiency and maintain thick film simultaneously. Specifically, synchronously manipulating crystallinity, domain size, and phase segregation to a suitable level are extremely challenging. Herein, a derivative of benzodithiophene terthiophene rhodanine (BTR) (a successful small molecule donor for thick-film OSCs), namely, BTR-OH, is synthesized with similar chemical structure and absorption but less crystallinity relative to BTR, and is employed as a third component to construct BTR:BTR-OH:PC 71 BM ternary devices. The power conversion efficiency (PCE) of 10.14% and fill factor (FF) of 74.2% are successfully obtained in ≈300 nm OSC, which outperforms BTR:PC 71 BM (9.05% and 69.6%) and BTR-OH:PC 71 BM (8.00% and 65.3%) counterparts, and stands among the top values for thick-film ASM OSCs. The performance enhancement results from the enhanced absorption, suppressed bimolecular/trap-assisted recombination, improved charge extraction, optimized domain size, and suitable crystallinity. These findings demonstrate that the donor derivative featuring similar chemical structure but different crystallinity provides a promising third component guideline for highperformance ternary ASM OSCs. Organic Solar Cells

Deciphering the Role of Fluorination: Morphological Manipulation Prompts Charge Separation and Reduces Carrier Recombination in All‐Small‐Molecule Photovoltaics

“…Similarly, the IDIC‐4F‐based BHJ film displays Rq of 1.88 nm, which is obviously larger than that of the IDIC‐based counterpart (1.43 nm). As the AFM phase images indicate, relative to the IDIC‐based BHJ film, the IDIC‐4F‐based blend film presents a uniform yet more obvious nanofibrillar network (Figure b,d), which is advantageous for both interface contact and charge transport (Table ). As shown in the TEM images, the IDIC‐4F BHJ film displays clear phase separation with a scale of ≈25 nm and a clear donor/acceptor interpenetrating network, which facilitates exciton dissociation and charge transport.…”

“…Traditional ASM OSCs consist of a small‐molecule electron donor (typically based on donor moieties using benzodithiophene [BDT], thiophene, dithienosilole [DTS], and indacenodithiophene [IDT], etc. ) and fullerene derivatives as electron acceptors (e.g., PC 61 BM and PC 71 BM), which have resulted in an over 11% power conversion efficiency (PCE) due to the concerted efforts in rational molecular design and device engineering . However, fullerene acceptors suffer from several drawbacks, such as their weak absorption in the visible and near‐infrared (NIR) range, limited tunability of energy levels, and poor thermal stability.…”

Ternary Organic Solar Cell with a Near‐Infrared Absorbing Selenophene–Diketopyrrolopyrrole‐Based Nonfullerene Acceptor and an Efficiency above 10%

“…The E loss values for OSCs based on SVA‐treated SM1:MPU4 and SM1:MPU1 are 0.42 and 0.53 eV, respectively. These values are amongst the lowest for any small‐molecule OSC, since the E loss in the BHJ‐based OSCs can be reduced by decreasing the energy offsets in the either HOMO or the LUMO offsets between the electron donor and acceptor units used in the BHJ active layer . The LUMO energy levels of MPU4 and MPU1 are similar (Table ).…”

“…In the past, most of ternary OSCs were based on conjugated polymers as donor but there are limited reports on all‐small‐molecule ternary OSCs. Recently, Tang et al have reported all‐small‐molecule ternary OSCs based on a small‐molecule donor and PC 71 BM and NFA, and achieved an overall PCE of 10.14% . The weight ratio between MPU4 and PC 71 BM was altered while keeping the weight ratio of SM1 constant.…”

Fluorination Effect for Highly Conjugated Alternating Copolymers Involving Thienylenevinylene-Thiophene-Flanked Benzodithiophene and Benzothiadiazole Subunits in Photovoltaic Application

“…Of all the third generation solar cell technologies (i.e., organic solar cells, perovskite solar cells, and dye-sensitized solar cells, and so on), bulk-heterojunction (BHJ) polymer solar cells (PSCs) have attracted broad academic and industrial interests, because of attractive features including flexibility, lightweight, large area, low-cost production, and environmental friendliness [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The photovoltaic performance of BHJ PSCs was highly dependent on the semiconductor materials used as the photoactive layer.…”