Wisnu Tantyo Hadmojo

Geometrically controlled organic small molecule acceptors for efficient fullerene-free organic photovoltaic devices

Organic small molecule (SM) acceptors containing a perylene diimide (PDI) moiety, F2B-T2PDI and T2PDI are synthesized, and the effects of their molecular geometry on the performance of fullerene-free organic photovoltaic (OPV) devices are investigated. The SM acceptors possess a PDI–core–PDI structure in which the PDI wing is connected to conjugated core units. By incorporation of a 2,5-difluorobenzene (F2B) moiety within the core unit, the planarity of the conjugated core is enhanced and the energy levels of the SM acceptor are down-shifted. In terms of molecular geometry, the F2B-containing SM acceptor, F2B-T2PDI, has a rigid core, which can symmetrically align the two PDI wings and enhance molecular packing. As a result, improved electron transport and bulk heterojunction morphology of the active layers are achieved. Furthermore, the incorporation of the F2B moiety effectively down-shifts the HOMO energy level, preventing back-transfer of holes from the acceptor to the cathode and enhancing the absorption of complementary wavelengths of the donor polymer, PTB7-Th. Leveraged by the beneficial geometric and energetic effects from the incorporation of F2B units, the power conversion efficiency of fullerene-free OPV devices using F2B-T2PDI reached 5%, whereas that using T2PDI was 3.63%.

High-Efficiency Photovoltaic Devices using Trap-Controlled Quantum-Dot Ink prepared via Phase-Transfer Exchange

Colloidal-quantum-dot (CQD) photovoltaic devices are promising candidates for low-cost power sources owing to their low-temperature solution processability and bandgap tunability. A power conversion efficiency (PCE) of >10% is achieved for these devices; however, there are several remaining obstacles to their commercialization, including their high energy loss due to surface trap states and the complexity of the multiple-step CQD-layer-deposition process. Herein, high-efficiency photovoltaic devices prepared with CQD-ink using a phase-transfer-exchange (PTE) method are reported. Using CQD-ink, the fabrication of active layers by single-step coating and the suppression of surface trap states are achieved simultaneously. The CQD-ink photovoltaic devices achieve much higher PCEs (10.15% with a certified PCE of 9.61%) than the control devices (7.85%) owing to improved charge drift and diffusion. Notably, the CQD-ink devices show much lower energy loss than other reported high-efficiency CQD devices. This result reveals that the PTE method is an effective strategy for controlling trap states in CQDs.

Fullerene-Free Organic Solar Cells with an Efficiency of 10.2% and an Energy Loss of 0.59 eV Based on a Thieno[3,4-c]Pyrrole-4,6-dione-Containing Wide Band Gap Polymer Donor

Although the combination of wide band gap polymer donors and narrow band gap small-molecule acceptors achieved state-of-the-art performance as bulk heterojunction (BHJ) active layers for organic solar cells, there have been only several of the wide band gap polymers that actually realized high-efficiency devices over >10%. Herein, we developed high-efficiency, low-energy-loss fullerene-free organic solar cells using a weakly crystalline wide band gap polymer donor, PBDTTPD-HT, and a nonfullerene small-molecule acceptor, ITIC. The excessive intermolecular stacking of ITIC is efficiently suppressed by the miscibility with PBDTTPD-HT, which led to a well-balanced nanomorphology in the PBDTTPD-HT/ITIC BHJ active films. The favorable optical, electronic, and energetic properties of PBDTTPD-HT with respect to ITIC achieved panchromatic photon-to-current conversion with a remarkably low energy loss (0.59 eV).

Improved performance of dye-sensitized solar cells using dual-function TiO(2) nanowire photoelectrode.

A unique, hierarchically structured, aggregated TiO(2) nanowire (A-TiO(2)-nw) is prepared by solvothermal synthesis and used as a dual-functioning photoelectrode in dye-sensitized solar cells (DSSCs). The A-TiO(2)-nw shows improved light scattering compared to conventional TiO(2) nanoparticles (TiO(2)-np) and dramatically enhanced dye adsorption compared to conventional scattering particles (CSP). The A-TiO(2)-nw is used as a scattering layer for bilayer photoelectrodes (TiO(2)-np/A-TiO(2)-nw) in DSSCs to compare the cell performance to that of devices using state-of-the-art photoelectrode architectures (TiO(2)-np/CSP). The DSSCs fabricated using bilayers of TiO(2)-np/A-TiO(2)-nw show improved power conversion efficiency (9.1%) and current density (14.88 mA cm(-2)) compared to those using single-layer TiO(2)-np (7.6% and 11.84 mA cm(-2)) or TiO(2)-np/CSP bilayer structures (8.7% and 13.81 mA cm(-2)). The unique contribution of the A-TiO(2)-nw layers to the device performance is confirmed by studying the incident photon-to-current efficiency. The enhanced external quantum efficiencies at approximately 520 nm and 650 nm clearly reveal the dual functionality of A-TiO(2)-nw. These unique properties of A-TiO(2)-nw may be applied in other devices utilizing light-scattering n-type semiconductor.

Development of n-Type Porphyrin Acceptors for Panchromatic Light-Harvesting Fullerene-Free Organic Solar Cells

The development of n-type porphyrin acceptors is challenging in organic solar cells. In this work, we synthesized a novel n-type porphyrin acceptor, PZn-TNI, via the introduction of the electron withdrawing naphthalene imide (NI) moiety at the meso position of zinc porphyrin (PZn). PZn-TNI has excellent thermal stability and unique bimodal absorption with a strong Soret band (300–600 nm) and weak Q-band (600–800 nm). The weak long-wavelength absorption of PZn-TNI was completely covered by combining the low bandgap polymer donor, PTB7-Th, which realized the well-balanced panchromatic photon-to-current conversion in the range of 300–800 nm. Notably, the one-step reaction of the NI moiety from a commercially available source leads to the cheap and simple n-type porphyrin synthesis. The substitution of four NIs in PZn ring induced sufficient n-type characteristics with proper HOMO and LUMO energy levels for efficient charge transport with PTB7-Th. Fullerene-free organic solar cells based-on PTB7-Th:PZn-TNI were investigated and showed a promising PCE of 5.07% without any additive treatment. To the best of our knowledge, this is the highest PCE in the porphyrin-based acceptors without utilization of the perylene diimide accepting unit.

11% Organic Photovoltaic Devices Based on PTB7‐Th: PC71BM Photoactive Layers and Irradiation‐Assisted ZnO Electron Transport Layers

Abstract The enhancement of interfacial charge collection efficiency using buffer layers is a cost‐effective way to improve the performance of organic photovoltaic devices (OPVs) because they are often universally applicable regardless of the active materials. However, the availability of high‐performance buffer materials, which are solution‐processable at low temperature, are limited and they often require burdensome additional surface modifications. Herein, high‐performance ZnO based electron transporting layers (ETLs) for OPVs are developed with a novel g‐ray‐assisted solution process. Through careful formulation of the ZnO precursor and g‐ray irradiation, the pre‐formation of ZnO nanoparticles occurs in the precursor solutions, which enables the preparation of high quality ZnO films. The g‐ray assisted ZnO (ZnO‐G) films possess a remarkably low defect density compared to the conventionally prepared ZnO films. The low‐defect ZnO‐G films can improve charge extraction efficiency of ETL without any additional treatment. The power conversion efficiency (PCE) of the device using the ZnO‐G ETLs is 11.09% with an open‐circuit voltage (V OC), short‐circuit current density ( J SC), and fill factor (FF) of 0.80 V, 19.54 mA cm‐2, and 0.71, respectively, which is one of the best values among widely studied poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐6‐diyl)]: [6,6]‐phenyl‐C71‐butyric acid methyl ester (PTB7‐Th:PC71BM)‐based devices.