Semitransparent organic solar cells were fabricated using lamination process. The devices were realized by using two independent substrates with transparent indium-tin-oxide electrode. One substrate was coated with poly(ethylenedioxy-thiophene)/poly(styrenesulfonate) layer and active layer of poly(3-hexylthiophene-2,5-diyl) (P3HT) and (6,6)-phenyl-C61 butyric acid methyl ester mixture. Another substrate was coated with ultra-thin polyethylenimine ethoxylated. The two substrates were laminated using hot press system. The device exhibited semitransparency and showed typical photovoltaic characteristics with open voltage of 0.59 V and short circuit current of 2.9 mA/cm2.

Highly conductive poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT,:,PSS) attracts a strong attention as a transparent electrode material since it may replace indium tin oxide (ITO) electrodes used in many organic semiconductor devices. However, PEDOT,:,PSS films have been usually deposited using acidic precursors, which caused long term device degradation as well as safety issues during device fabrication processes. This paper firstly reports application of highly conductive PEDOT,:,PSS films deposited on polyethylene terephthalate (PET) substrates using a neutralized precursor to organic bulkhetrojunction solar cells. The sheet resistance ($R_{s}$) of PEDOT,:,PSS was reduced by more than two orders of magnitudes by spin coating the neutralized solution containing 5% of dimethyl sulfoxide (DMSO) and dipping the films in DMSO for 30,min. Subsequently, an approximately 55 nm-thick PEDOT,:,PSS layer was obtained with $R_{s}$ =159 $Omega$/$square$, a conductivity of 1143 S/m, and an optical transmittance of 84%. A solar cell based on poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b$'$]dithiophene-2,~6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,~4-b]thiophenediyl]: [6,6]-phenyl-C$_{71}$-butyric acid methyl ester fabricated on the PEDOT: PSS/PET substrate exhibited a higher open circuit voltage and power conversion efficiency than did a control solar cell fabricated on an ITO-coated PET substrate. These results suggest that the highly conductive PEDOT,:,PSS films may contribute to realize ITO-free flexible organic solar cells.

We characterized bulk-heterojunction (BHJ) solar cells using a new phenylene-thiophene oligomer, 3,7-bis[5-(4-n-hexylphenyl)-2-thienyl]dibenzothiophene-5,5-dioxide (37HPTDBTSO), and phenyl-C61-butyric-acid methyl ester (PCBM). Their photovoltaic properties including current-voltage characteristics and spectrum response were investigated. It was found that 37HPTDBTSO is appraised to be valuable electron donor. The characteristics of BHJ solar cells using mixed two donors of 37HPTDBTSO and a polymer of poly(3-hexylthiophene) (P3HT) were further investigated. OSC using the blend film of mixed donars and PCBM achieved a power conversion efficiency of 0.89%.

We present an optimization algorithm for the design of multilayer antireflection (AR) coatings for organic photovoltaic (OPV) cells. When a set of available materials for the AR films is given, the proposed method allows for searching the globally optimized AR structure that maximizes the short-circuit current density (JSC) under simulated solar light illumination (AM 1.5). By applying this method to an OPV solar cell with a configuration of Al/P3HT:PCBM/MoO3/ITO, we demonstrated that JSC can increase by 7.5% with a 6-layer AR coating, consisting of MgF2, ZnS, and Al2O3. A notable feature of this method is that it can find not only the optimal solution, which maximizes JSC , but also the quasi-optimal solutions, which increase JSC to nearly maximum levels. We showed that the quasi-optimal solution may have higher robustness against deviations in film thicknesses, from their designated values. This method indicates the importance of practically useful, non-optimal solutions for designing AR coatings. The present method allows for extending the user's choices and facilitates the realization of a practical design for an AR coating.

We fabricated organic p-n heterojunction, p-i-n heterojunction and all-i-layer photovoltaic cells of a zinc phthalocyanine (ZnPc)/1:1 codeposition (ZnPc:C60)/C60 structure with Al cathode. We investigated the effects of the device structure and the cathode material on the photovoltaic properties. The thickness of the i-layer was changed as 0 nm (= p-n heterojunction), 10 nm (= p-i-n heterojunction) or 50 nm (= all-i-layer) with the total thickness of 50 nm. We also changed cathode materials from Al to low-workfunction Mg:Ag electrode. Photovoltaic properties, i.e., short-circuit current density, fill factor and power conversion efficiency, were strongly influenced by the device structure and cathode material. Finally, the power conversion efficiency showed a maximum (1.5%) with the p-i-n structure and a Mg:Ag cathode under Air Mass 1.5 global solar conditions.