Structural modifications of zinc phthalocyanine thin films for organic photovoltaic applications

Zinc phthalocyanine (ZnPc) thin films are vacuum-evaporated on bare indium-tin-oxide (ITO) coated glass by varying substrate temperature and growth rate. The samples are characterized by atomic force microscopy, x-ray diffraction, and infrared spectroscopy. The temperature does not play a clear role in the crystalline growth of ZnPc possibly due to the significant structural defects on ITO surface, while it strongly influences the surface morphology and molecular alignment. The relationships between growth characteristics and performances of photovoltaics with planar heterojunction are discussed in detail. Increasing temperature or growth rate leads to a rougher surface morphology, which enables more donor/accepter interface area for photocurrent generation. Moreover, at elevated temperature, more molecules adopt standing-up geometry, resulting in a reduction in overall efficiency. The results imply that low-temperature process in order to control the molecular alignment is preferred for efficient organic photovoltaics. By simply increasing the growth rate of ZnPc up to 0.40 Å/s at room temperature, ZnPc/C60 planar heterojunction shows an efficiency of 1.66, compared to 1.24 for the cell when ZnPc is prepared at 0.10 Å/s. © 2012 American Institute of Physics

Interpenetrating heterojunction photovoltaic cells based on C60 nano-crystallized thin films

An interpenetrating heterojunction (IHJ) structure facilitates efficient charge separation and transport in the active layer of organic photovoltaic cells (OPVs). Additionally, the recombination of generated carriers in IHJs is reduced as these networks exhibit high carrier transport with minimal recombination sites. We have developed a simple method to fabricate nanocrystallized fullerene (C60) films, which are produced by subjecting evaporated C60 films to either solvent spin-coating or solvent vapor annealing (SVA). The size of the rod-shaped nanocrystals in the films were controlled by changing the solvent and annealing time. An 80-nm-diameter size nanocrystallized C60 film that was fabricated using SVA with ethanol was incorporated as an acceptor material in an inverted IHJ OPV cell. Tetraphenyldibenzoperiflanthene (DBP) was evaporated onto the nanocrystallized C60 film as the donor material. The power conversion efficiency of an IHJ OPV cell (ITO/TiOx/nanocrystallized C60 film/DBP/MoO3/Au) increased from 1.79% to 2.12%, when compared with the conventional PHJ OPV cell. © 2016 Elsevier B.V.Embargo Period 24 month

Effect of the solvent used to prepare the photoactive layer on the performance of inverted bulk heterojunction polymer solar cells

The initial performance and subsequent degradation of inverted polymer solar cells [indium–tin oxide/titanium oxide (TiO x )/[6,6]-phenyl C61 butyric acid methyl ester (PCBM): regioregular poly(3-hexylthiophene) (P3HT)/poly(3,4-ethylenedioxylenethiophene):poly(4-styrene sulfonic acid)/Au, TiO x cell] are studied by photocurrent–voltage measurements as well as ac impedance spectroscopy (IS) and carrier mobility measurements. The TiO x cells containing a P3HT:PCBM layer prepared from a solution of chlorobenzene (CB) showed a maximum power conversion efficiency (PCE) of 2.23%. In contrast, the TiO x cells containing a P3HT:PCBM layer prepared from a solution of 1,2,3,4-tetrahydronaphthalene (tetralin) containing 2 vol % 1,8-octanedithiol (ODT) exhibited a maximum PCE of 2.92%. However, after exposure to light irradiation for 100 h, the maximum PCE of the tetralin:ODT cell decreased to 68% of its initial value. On the other hand, over 96% of the maximum PCE was maintained in the CB cell after 100 h of irradiation. The IS measurement results suggest that the degradation of the Tetralin:ODT cell was caused by a morphological change of the P3HT:PCBM layer that made efficient photoinduced charge separation difficult.</jats:p

Effect of the solvent used to prepare the photoactive layer on the performance of inverted bulk heterojunction polymer solar cells

The initial performance and subsequent degradation of inverted polymer solar cells [indium-tin oxide/titanium oxide (TiOx)/[6,6]-phenyl C61 butyric acid methyl ester (PCBM): regioregular poly(3-hexylthiophene) (P3HT)/poly(3,4-ethylenedioxylenethiophene):poly(4- styrene sulfonic acid)/Au, TiOx cell] are studied by photocurrent-voltage measurements as well as ac impedance spectroscopy (IS) and carrier mobility measurements. The TiOx cells containing a P3HT:PCBM layer prepared from a solution of chlorobenzene (CB) showed a maximum power conversion efficiency (PCE) of 2.23%. In contrast, the TiOx cells containing a P3HT:PCBM layer prepared from a solution of 1,2,3,4- tetrahydronaphthalene (tetralin) containing 2 vol- 1,8-octanedithiol (ODT) exhibited a maximum PCE of 2.92%. However, after exposure to light irradiation for 100 h, the maximum PCE of the tetralin:ODT cell decreased to 68% of its initial value. On the other hand, over 96% of the maximum PCE was maintained in the CB cell after 100 h of irradiation. The IS measurement results suggest that the degradation of the Tetralin: ODT cell was caused by a morphological change of the P3HT:PCBM layer that made efficient photoinduced charge separation difficult. © 2014 The Japan Society of Applied Physics

"Phase separation of co-evaporated ZnPc:C

We demonstrate phase separation of co-evaporated zinc phthalocyanine (ZnPc) and fullerene (C 60) for efficient organic photovoltaic cells. With introducing a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film and a crystalline copper iodide film on indium tin oxide, 20-nm-thick ZnPc film adopts a lying-down crystalline geometry with grain sizes of about 50 nm. This surface distributed with strong interaction areas and weak interaction areas enables the selective growth of ZnPc and C 60 molecules during following co-evaporation, which not only results in a phase separation but also improve the crystalline growth of C 60. This blend film greatly enhances the efficiencies in photocurrent generation and carrier transport, resulting in a high power conversion efficiency of 4.56 under 1 sun. © 2012 American Institute of Physics

Development of bifacial inverted polymer solar cells using a conductivity-controlled transparent PEDOT: PSS and a striped Au electrode on the hole collection side

An inverted bifacial polymer solar cell was developed using a conductivity-controlled transparent poly(3,4-ethylenedioxylenethiophene):poly(4- styrene sulfonic acid) (PEDOT:PSS) as a hole collection layer and a striped Au electrode with a large open aperture ratio (Rap) as a hole collection electrode. We investigated the performance of the device by varying the interelectrode distance of the striped Au electrode and the sheet resistance of the PEDOT:PSS film. The device using untreated Clevios P (PEDOT:PSS) showed a maximum electric output (Pw) in the Rap range of 50 to 65%. When alcohol-treated Clevios P (Clevios P+) with a lower electrical resistance was used, the maximum Pw increased by 40% compared with that of the device using Clevios P. The maximum Pw was obtained in the R ap range of 84% as the hole collection efficiency of the striped Au electrode improved with the decreased sheet resistance of the PEDOT:PSS. © 2014 The Japan Society of Applied Physics

Mechanistic investigation into the light soaking effect observed in inverted polymer solar cells containing chemical bath deposited titanium oxide

In the glass-indium tin oxide (ITO)/titanium oxide (TiOx)/regioregular poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61 butyric acid methyl ester (PCBM)/poly(3,4-ethylenedioxylenethiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS)/Au cell (TiOx cell), which contains amorphous titanium oxide prepared by chemical bath deposition and dried at 150 °C, a light soaking effect has been observed upon irradiation with white light. In contrast, in ITO/titanium oxide (TiO2)/P3HT:PCBM/PEDOT:PSS/Au cell (TiO2 cell), which contains anatase titanium oxide prepared by heat treatment at 450 °C, the maximum power conversion efficiency was obtained just after irradiation with white light. The number of P3HT+• cation radicals in the quartz-ITO/TiOx and TiO2/P3HT:PCBM substrates was estimated by ESR measurements at room temperature upon irradiation with white light. It increased gradually with an increase in irradiation time for the TiOx substrate but increased only slightly just after light irradiation for the TiO2 substrate. Upon irradiation with UV-cut light, the performance of the TiOx cell was inferior to that of the TiO2 cell. This could be related to the resistances of the P3HT:PCBM layers which were estimated by alternating current impedance spectroscopy. The resistance of the P3HT:PCBM layer in the TiOx cell was much larger than that in the TiO2 cell, though the difference between the two cells was merely heat treatment temperature of titanium oxide films using as electron collection layers. That is, the concentration of photocarriers in the P3HT:PCBM of the TiOx cell was significantly less than that in the P3HT:PCBM of the TiO2 cell. From these experimental results, the light soaking effect could be reasonably explained by assuming the existence of charge recombination centers in the TiOx near the TiOx/P3HT:PCBM interface

高耐久有機太陽電池を可能にするπ-d相互作用を用いた相分離構造の制御

塗布系有機薄膜太陽電池は、いわゆる印刷と同様の製膜法であるため、製造コストが大型の装置が必要な真空蒸着に比べて1/10以下となる超低コスト太陽電池として期待されている。有機薄膜太陽電池は、p型n型半導体を混合するバルクヘテロ層に、添加剤を加えることで相分離を制御し高性能化する。添加剤により高性能化した太陽電池は、数百時間程度の光照射下で発電を行い続けると内部の相分離が時間とともに構造変化してしまい、性能が低下する問題があった。π共役-d軌道相互作用を用いた界面制御技術を応用すれば、添加剤を用いない相分離構造の制御が可能となる手法を開発した。Printed organic photovoltaic cells (OPVs) are expected to be ultra-low-cost solar cells with 1/10 production cost compared to vacuum deposition process for inorganic solar cells. Bulkheterojjunction structures in OPVs are controlled by adding an additive. Unfortunately, the additive becomes the problem that the performance is degraded. We have developed the interface control technology using π-conjugated-d orbital interaction that enables control of phase separation structure without using the additive.研究課題/領域番号:16K05882, 研究期間(年度):2016-04-01 - 2019-03-31出典：研究課題「高耐久有機太陽電池を可能にするπ-d相互作用を用いた相分離構造の制御」課題番号16K05882（KAKEN：科学研究費助成事業データベース（国立情報学研究所）） （https://kaken.nii.ac.jp/report/KAKENHI-PROJECT-16K05882/16K05882seika/）を加工して作