A solution to the problem of reduction of available photosynthetically active radiation (PAR) due to the cover with conventional opaque photovoltaics (PV) of greenhouses is the use of semitransparent PV. The question is how dense the semitransparent PV should be and how dense the coverage should be in order not to burden plant growth. The present paper assesses the effect of the use of semitransparent organic photovoltaics (OPV) on the greenhouse roof cover on the available PAR inside the greenhouse. The method used is to simulate the transmission of radiation through the cover and into the greenhouse with computational fluid dynamics (CFD) using the discrete ordinates (DO) model. Three combinations of OPV/cover that give a normal (perpendicular) transmittance to PAR of 30%, 45%, and 60%, defining the required PV covering, were examined. Then the radiation transmission during eight indicative solar days was simulated. The results are given in terms of available PAR radiation inside the greenhouse and of crop photosynthesis rate, comparing them with the results of a polyethylene cover without OPVs and external conditions. The reduction observed to the mean daily PAR radiation integral for the cases with normal PAR transmittance of 30%, 45%, and 60% in relation to the bare polyethylene (PE) was 77%, 66%, and 52%, respectively while the respective simulated reduction to the daily average photosynthesis rate was 33%, 21%, and 12%, respectively. Finally, the yearly power production from the OPV per greenhouse length meter for the cases with normal PAR transmittance of 30%, 45%, and 60% was 323, 242, and 158 kWh m⁻¹ y⁻¹, respectively. The results of this work could be further used for the optimization of greenhouse design for maximizing the PAR at the crop level.

A novel approach for the fabrication of flexible organic photovoltaic (OPV) modules with an inverted architecture by gravure printing process is presented. The printing has been carried out using a sheet-to-sheet (S2S) lab scale proofer, while all the printing steps were performed in ambient conditions and optimized for each of the OPV layers. Commercially available Zinc Oxide (ZnO) ink was used as the electron transport (ETL) layer, poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM) blend comprised the bulk heterojunction (BHJ) photoactive layer, poly-3,4-ethylenedioxy-thiophene:poly(styrenesulfonic-acid) (PEDOT:PSS) was used as the hole transport layer (HTL), and silver (Ag) nanoparticle (NP) ink was used as the top contact electrode. The four OPV layers have been successively printed on indium tin oxide (ITO) coated polyethylene terephthalate (PET) flexible substrate using the same printing parameters. The OPV modules have size of 45 cm² with an active area of 8 cm² composed of 8 interconnected cells and exhibited a maximum power conversion efficiency (PCE) of over 2%. The printing parameters were optimized by the contribution of extensive morphological characterization by scanning and transmission electron microscopy (SEM, TEM), as well as from Spectroscopic Ellipsometry (SE) for the determination of the printed layers thickness, optical properties and photoactive layer blend morphology. The above approach reveals the required printing parameters for large-scale manufacturing of flexible OPVs by a R2R process.