Two solution-processable acceptor–donor–acceptor (A-D-A) structured organic molecules with bithienyl-substituted benzodithiophene (BDTT) as central and donor unit, indenedione (ID) as acceptor unit and end groups, and thiophene (T) or bithiophene (bT) as π-bridges, D1 and D2, are designed and synthesized for the application as donor materials in organic solar cells (OSCs). Two corresponding molecules with alkoxy side chains on BDT, DO1, and DO2 are also synthesized for comparison. The four compounds possess broad absorption covering the wavelength range 450–740 nm and relatively lower HOMO energy levels from −5.16 to about −5.19 eV. D2 and DO2 with bithiophene π-bridges demonstrate stronger absorbance and higher hole mobilities than the compounds with thiophene π-bridges. The power conversion efficiency (PCE) values of the OSCs based on the organic compounds/PC70BM (1.5:1, w/w) are 6.75% for D2, 5.67% for D1, 5.11% for DO2, and 4.15% for DO1. The results indicate that the molecules with thienyl conjugated side chains and bithiophene π-bridges show better photovoltaic performance. The PCE of the D2-based OSC are among the highest values in the OSCs based on the solution-processed organic small molecules.

Two novel porphyrin-polythiophene star-shaped polymer (P-bs1 and P-bs2) containing triphenylamine terminated poly(3 0 -hexyl-2,2 0 -bithiophene) and poly(3 0 -hexyl-2,2 0 -bithiophene) as four arms in the peripheral of porphyrin core were synthesized by Stille reaction. The thermal, photophysical, electrochemical and photovoltaic properties of the porphyrin-polythiophene derivatives were investigated. The porphyrin-polythiophene derivatives showed broad absorption in the region of 350 $ 650 nm. In particular, the absorption intensity at 450 $ 650 nm was greatly enhanced for the meso-substituted polythiophene derivatives, P-bs2. The photoluminescence spectra indicated that the emission peaks of porphyrin units were suppressed by the intensive emission of thiophene units. The electrochemical properties indicated that the porphyrin-polythiophene derivatives are potential electron-donor materials for bulk heterojunction solar cells and dye-sensitized solar cells (DSSCs). Polymer bulk heterojunction solar cells based on P-bs2 : PCBM (1 : 1, w/w) showed power conversion efficiencies (PCE) up to 0.61% under the illumination of AM 1.5, 100 mW cm À2 , which increased by 69% compared to that of P-bs1 (0.36%). Meanwhile, higher PCE of 2.17% and 3.91% based on P-bs1 and P-bs2 polymer-sensitized solar cells were attained. The better photovoltaic properties benefited from longer arms of polythiophene derivatives.

Rational molecular design of conjugated polymers and cautious optimization of morphologies of the active layer are critical for developing high performance polymer solar cells (PSCs). In this work, we designed and synthesized a new thiophene monomer TBTF attaching donor−acceptor (D−A) conjugated side chain with fluorinated 4,7-dithien-5-yl-2,1,3-benzodiathiazole (BTF) as acceptor unit, and synthesized two new two-dimension-conjugated (2D-conjugated) copolymers, P(BDT-TBTF) and P(BDT-TBTF/DPP), for the application as donor materials in PSCs. P(BDT-TBTF) is a new side chain D−A copolymer of benzodithiophene (BDT) and TBTF units, and P(BDT-TBTF/DPP) is a ternary D−A copolymer of BDT, TBTF and pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) units. The introduction of TBTF unit with D−A conjugated side chain and DPP unit forming the ternary copolymer provides the opportunity to tune the optoelectronic properties of the resulting polymers. As expected, the binary copolymer P(BDT-TBTF) shows an enhanced absorption coefficient and lower-lying HOMO energy level, and the ternary copolymer P(BDT-TBTF/DPP) possesses a small bandgap and quite broad absorption band matched well with solar spectrum. These features are beneficial to achieving reasonable high short-circuit current (J sc ) and high open-circuit voltage (V oc ). Bulk-heterojunction PSCs based on P(BDT-TBTF) showed an initial power conversion efficiency (PCE) of 5.66% with a high V oc of 0.88 V and a J sc of 11.23 mA cm −2 , whereas P(BDT-TBTF/DDP) gave a PCE of 3.51% along with a higher J sc of 13.15 mA cm −2 . The J sc and PCE of the devices were further improved by a simple methanol treatment, to 13.21 mA cm −2 and 6.21% for P(BDT-TBTF) and 14.56 mA cm −2 and 5% for P(BDT-TBTF/DPP), respectively. To the best of our knowledge, the PCE of 6.21% is the highest value reported for PSCs based on side chain D−A copolymers to date. This is a good example for a subtle tuning absorption properties, energy levels, charge transport and photovoltaic properties of the polymers by rational molecular design.

Three novel organic dyes based on porphyrin derivatives were designed and synthesized for dye-sensitized solar cells, resulting in a maximum power conversion efficiency (eta) of 5.14% and a maximum IPCE value of 72% for a cell based on the dye.

Two novel branchlike organic dyes (D1 and D2) comprising two di(p-toyl)phenylamine moieties as the electron donor, cyanoacetic acid moieties as the electron acceptor, thiophene or 3-hexylthiophene moieties as the Π-spacer, were designed and synthesized for dye-sensitized solar cells (DSSCs). It was found that the introduction of two di(p-tolyl)phenylamine groups to form the branchlike configuration exhibited better photovoltaic performance due to the improvement of the electron donating and the light-harvesting properties. By the introduction of two di(p-tolyl)phenylamine groups into the framework of D2, it is interesting to note that the UV-vis absorption of D2 showed an obvious blue-shift but also improved molar extinction coefficient compared with that of D3. The transient absorption measurements showed that the dyes D1 and D2 with two di(p-tolyl)phenylamine-substitutes could effectively retard charge recombination between electrons at the TiO 2 and the oxidized dyes. Among the three dyes studied, a maximum power conversion efficiency of 6.41% was obtained under simulated AM 1.5 G solar irradiation (100 mW/cm 2 ) with a DSSC based on D2 dye (J sc ) 11.62 mA/cm 2 , V oc ) 0.73 V, FF ) 0.756) upon the addition of 1.0 × 10 -3 M chenodeoxycholic acid (CDCA) as coadsorbent.

Efficient semitransparent polymer solar cells (ST-PSCs) have been fabricated with one-dimensional photonic crystals (1DPCs) as a high reflector. The 1DPCs are composed of several pairs of WO3 (65.8 nm)/LiF (95.5 nm). By optimizing the pairs of WO3/LiF, 1DPCs can reflect the light back into the ST-PSCs due to the photonic band gap, when the high reflectance range of 1DPCs is matched with absorption spectrum of the active layer. ST-PSCs with 8 pairs of 1DPC exhibit an attractive performance. The short-circuit current density (Jsc) and power conversion efficiency (PCE), respectively, reach to 9.76 mA/cm(2) and 5.16% compared to 8.12 mA/cm(2) and 4.24% of the reference ST-PSCs without 1DPCs. A maximum enhancement of 20.2% in Jsc is obtained and the PCE increases by ~21.7%. This approach provides a simple, fascinating and promising method to realize the highly efficient ST-PSCs toward applications.

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Semitransparent polymer solar cells (ST-PSCs) show attractive potential in power-generating windows or building-integrated photovoltaics. However, the development of ST-PSCs is lagging behind opaque PSCs because of the contradiction between device efficiency and transmission. Herein, Ag/Au alloy nanoparticles and photonic crystals (PCs) were simultaneously introduced into ST-PSCs, acting compatibly as localized surface plasmon resonances and distributed Bragg reflectors to enhance light absorption and transmission. As a result, ST-PSCs based on a hybrid PTB7-Th:PCBM active layer contribute an efficiency as high as 7.13 ± 0.15% and an average visible transmission beyond 20%, which are superior to most of the reported results. Furthermore, PCs can partly compensate valley range of transmission by balancing reflection and transmission regions, yielding a high color rendering index of 95. We believe that the idea of two light management methods compatibly enhancing the performance of ST-PSCs can offer a promising path to develop photovoltaic applications.