The unique electro‐optical features of organic photovoltaics (OPVs) have led to their use in applications that focus on indoor energy harvesters. Various adoptable photoactive materials with distinct spectral absorption windows offer enormous potential for their use under various indoor light sources. An in‐depth study on the performance optimization of indoor OPVs is conducted using various photoactive materials with different spectral absorption ranges. Among the materials, the fluorinated phenylene‐alkoxybenzothiadiazole‐based wide bandgap polymer—poly[(5,6‐bis(2‐hexyldecyloxy)benzo[c][1,2,5]thiadiazole‐4,7‐diyl)‐alt‐(5,50‐(2,5‐difluoro‐1,4‐phenylene)bis(thiophen‐2‐yl))] (PDTBTBz‐2Fanti)‐contained photoactive layer—exhibits a superior spectrum matching with indoor lights, particularly a light‐emitting diode (LED), which results in an excellent power absorption ratio. These optical properties contribute to the state‐of‐the‐art performance of the PDTBTBz‐2Fanti:[6,6]‐phenyl‐C71 butyric acid methyl ester (PC71BM)‐based OPV with an unprecedented high power‐conversion efficiency (PCE) of 23.1% under a 1000 lx LED. Finally, its indoor photovoltaic performance is observed to be better than that of an interdigitated‐back‐contact‐based silicon photovoltaic (PCE of 16.3%).

A new series of wide band gap photovoltaic polymers based on a fluorinated phenylene-alkoxybenzothiadiazole unit with an optical band gap of over 1.90 eV are designed and utilized for high-performance single- and multi-junction bulk heterojunction polymer solar cells.

No abstract

No abstract

A series of new conjugated polymers based on the asymmetric benzo[1,2-b:4,5-b′]dithiophene (BDT) unit were designed and synthesized for use in bulk-heterojunction polymer solar cells. Each side chain of the BDT was tuned by introducing alkyl and alkoxy groups. The best solar cell efficiency was achieved in an asymmetric polymer device based on 4-octyl-8-octyloxy-BDT (7.64% PCE), which performed better than devices based on the symmetric dioctyl-BDT (6.48% PCE) or dioctyloxy-BDT (7.18% PCE). Further modification of the side chains, replacing octyloxy with butoxydiethoxy, improved the PCE to 8.12% due to the enhanced hole mobility, hole/electron mobility balance, and formation of tight contacts with the PEDOT:PSS layer. The effects of the side chains on the polymer HOMO energy levels and photovoltaic parameters were investigated. ■ INTRODUCTIONBenzo[1,2-b:4,5-b′]dithiophene (BDT) derivatives are among the most widely used electron-donating units in the polymer backbones of polymer solar cells (PSCs). A variety of electronaccepting units including thieno [3,4-c]pyrrole-4,6-dione, 1 2,1,3-benzothiadiazole, 2,3 quinoxaline, 4 diketopyrrolopyrrole, 5 and thieno[3,4-b]thiophene 6−11 can provide photoconversion efficiencies (PCEs) exceeding 8% through the use of alternating copolymers by coupling with BDT unit. The most commonly used derivative in the BDT family is 4,8-dialkoxy-substituted BDT. This group has been used because its synthesis is easy and some dialkoxy-BDT polymers provide excellent PCEs. 12−17 Polymers derived from the copolymerization of fluorinated thieno[3,4-b]thiophene (TT) and BDT, TT-BDT, provide good OPV performances in various device structures. 6,9,18−24 These finding led us to use the TT-BDT backbone as a structural platform for investigating the structure/property relationship in an effort to identify new polymers that can improve solar cell performances. 25 The photovoltaic performances of a polymer may be improved by structurally modifying BDT through the introduction of novel substituents, as demonstrated in many research groups (see Figure 1). Liang et al. achieved a HOMO level that was 0.1 eV deeper than the level obtained from the dioctyloxy-BDT polymer by introducing dioctyl-BDT into the polymer backbone; thus, a 0.1 V higher open circuit voltage (V oc ) was achieved in the solar cell device. 15 Lee et al. replaced oxygen atoms with sulfur atoms in the side chains to reduce the HOMO energy level of the conjugated polymer from −5.31 to −5.41 eV and increase V oc from 0.83 to 0.99 V. 26 Bathula et al. polymerized TIPS-substituted BDT with a thieno[3,4-b]-thiophene ester to obtain a deeper HOMO level, thereby increasing the V oc of the resulting PSC to 0.82 V. 27 Wung et al. characterized a polymer of DPP, prepared with unsubstituted-BDT, to achieve a HOMO energy level of −5.46 eV, which was deeper than the −5.29 eV level of the dialkoxy-BDT. 28 Several groups have reported obtaining high V oc s and PCEs by replacing alkoxy side chains with aryl groups. 2,11,29,30 Alkyl side chains offer a...

The fullerene-based PSCs based on novel PNTz4T-1F polymer processed from a halogen-free solvent system demonstrated an outstanding PCE of 11.77% due to the optimum molecular ordering/packing and morphology.

Semi-transparent plastic solar cells are currently highly attractive for their potential as the most prominent components for building-integrated photovoltaics. However, the power conversion efficiency (PCE) of semi-transparent plastic solar cells still lags behind due to the lack of a suitable transparent top electrode which can be easily fabricated. Here, we demonstrate high performance semi-transparent plastic solar cells by introducing an oxide-metal-oxide (OMO) multilayer composed of MoO 3 and Ag as a transparent top electrode. Because the conductivity of the OMO electrode is governed by an intermediate Ag layer sandwiched between 2 MoO 3 layers, the PCE also strongly depends on the thickness of the intermediate Ag layer in the OMO electrode. By controlling the thickness of Ag layer, we obtained various PCE values from 4.5% with~50% maximum transparency in the visible region to 9.1% with~5% maximum transparency in the visible region. In addition, in order to get closer to practical application, 2 sizes of mini-module devices were fabricated on a larger (10.0 cm × 10.0 cm) substrate for outdoor operation and small-sized (7.0 cm × 5.0 cm) substrates for indoor operation were demonstrated using 3 materials of different color.

A series of D–A1–D–A2 type regioregular copolymers based on difluorobenzothiadiazole (DFBT) and dialkoxybenzothiadiazole (ROBT) structures for high performance PSCs.