Akinobu Hayakawa

High performance polythiophene/fullerene bulk-heterojunction solar cell with a TiOx hole blocking layer

Insertion of a TiOx layer between the Al electrode and the active layer of an organic photovoltaic cell resulted in a high performance with 94% durability under irradiation (100mW∕cm2) for 100h and had improved fill factor and open circuit voltage. An efficiency of 4.05% was achieved by using the cell containing a TiOx layer fabricated and measured in ambient atmosphere. The TiOx layer works as an effective barrier to physical damage and chemical degradation, resulting in high durability under aerobic conditions, and also serves as a hole blocking layer, resulting in improved parallel resistance and rectification.

Enhanced Efficiency and Stability in P3HT:PCBM Bulk Heterojunction Solar Cell by using TiO2 Hole Blocking Layer

Insertion of TiO 2 layer between Al negative electrode and active layer of bulk-heterojunction gave a high solar conversion efficiency and high stability. The TiO 2 layer was prepared by spin-coating titanium(IV)isopropoxide (Ti(OC 3 H 7 ) 4 ) on active layer of blended P3HT:PCBM. The parallel resistance (Rp) is increased by inserting TiO 2 layer leading to an increase in Voc. The TiO 2 layer works as a hole blocking layer and prevents the physical and chemical damages by the direct contact between P3HT:PCBM active layer and Al electrode resulting in improvement of the parallel resistance and rectification. The efficiency of P3HT:PCBM bulk heterojunction cell with TiO 2 hole blocking layer attained 4.05% with a Isc 9.72 mA/cm 2 , Voc 0.60 V, and FF 0.70 by using optimized TiO 2 film thickness and ratio of P3HT:PCBM condition.

(Invited) Organic-Inorganic Hybrid Solar Cells with Antimony Sulfide-Metal Composites

Organic-inorganic hybrid solar cells composed of glass/F-doped SnO2/TiO2/La-decorated or Zn-doped Sb2S3/ poly[(3-hexylthiophene)-2,5-diyl]/poly[3-(3-carboxypropyl)thiophene-2,5-diyl]/Au have been prepared and evaluated their photovoltaic performance. Using La-decorated Sb2S3 for hybrid solar cell resulted in 33% improvement of power conversion efficiency (PCE) as compared to that of the non-decorated Sb2S3 because of lowering the resistance at the interface, which was confirmed by the impedance analyses. It was found that the added La was phase-separated and accumulated between the layers of TiO2 and Sb2S3. While doping of Zn into Sb2S3 resulted in the enlargement of the crystallite size of Sb2S3 from 14 nm to 25 nm. Utilization of Zn-doped Sb2S3 for hybrid solar cell attained 57% enhancement of PCE. This result is ascribed to the effective lowering the bulk-resistance.

Improvement of device performance by using zinc oxide in hybrid organic–inorganic solar cells

Zinc oxide (ZnO) nanopowder was applied to hybrid solar cells in combination with poly(3-hexylthiophene). Stability tests of the hybrid solar cell with or without encapsulation with glass and UV cut-off films were performed under 1 sun at 63 °C at a relative humidity of 50%. It was found that the sealed cell showed worse device performance in terms of the loss of the open-circuit voltage (Voc), whereas the unsealed cell exposed to air retained an almost constant Voc for more than 3 d under dark and atmospheric conditions. Placement in O2 atmosphere in the dark led to the recovery of Voc. Cation (Sn4+) doping into ZnO was performed, and the loss of Voc was effectively suppressed through the restraint of the supply of the excited electron from the valence band to the conduction band.