Krebs et al. Scalable, ambient atmosphere roll-to-roll manufacture of encapsulated large area, fl exible organic tandem solar cell modules

We present a cost analysis based on state of the art printing and coating processes to fully encapsulated, flexible ITO-and vacuum-free polymer solar cell modules. Manufacturing data for both single junctions and tandem junctions are presented and analyzed. Within this calculation the most expensive layers and processing steps are identified. Based on large roll-to-roll coating experiments the exact material consumptions were determined. In addition to the data for the pilot scale experiment presented here, projections to medium and large scale scenarios serve as a guide to achieve cost targets of 5 Vct per W p in a detailed material and cost analysis. These scenarios include the replacement of cost intensive layers, as well as process optimization steps. Furthermore, the cost structures for single and tandem devices are listed in detail and discussed. In an optimized model the material costs drop below 10 V per m 2 which proves that OPV is a competitive alternative to established power generation technologies. Broader contextAmong the emerging solar cell technologies organic photovoltaics (OPVs) have gained enormous attraction due to their various advantages in applications, i.e. light weight, semitransparency, tunable band gaps and colors. The decisive criteria for a market entrance of a new renewable technology to become a successful competitor are the costs and cost potential which are inuenced by their processing technique. Currently processing of photovoltaic devices is mainly done in non-continuous batch-to-batch processes at elevated temperatures. OPVs offer the advantage of high throughputs due to their compatibility to continuous rollto-roll coating techniques. This leads to the potential to dramatically reduce the processing costs in comparison to mature photovoltaic technologies. One of the drawbacks of OPVs is their lower device efficiency in comparison to inorganic materials. The use of tandem devices offers the potential to overcome the limiting device efficiency of OPVs which requires the printing of several additional layers. Based on state of the art processing costs the exact material consumptions for single and tandem devices were determined and compared. We demonstrate that OPV is a competitive energy technology which is not only compatible with inorganic PV, but also with other energy technologies such as wind, hydro and biomass.

We describe the fabrication of roll-to-roll (R2R) printed organic photovoltaic (OPV) modules using gravure printing and rotary screen-printing processes. These two-dimensional printing techniques are differentiating factors from coated OPVs enabling the direct patterning of arbitrarily shaped and sized features into visual shapes and, increasing the freedom to connect the cells in modules. The inverted OPV structures comprise five layers that are either printed or patterned in an R2R printing process. We examined the rheological properties of the inks used and their relationship with the printability, the compatibility between the processed inks, and the morphology of the R2R-printed layers. We also evaluate the dimensional accuracy of the printed pattern, which is an important consideration in designing arbitrarily-shaped OPV structures. The photoactive layer and top electrode exhibited excellent cross-dimensional accuracy corresponding to the designed width. The transparent electron transport layer extended 300 µm beyond the designed values, whereas the hole transport layer shrank 100 µm. We also examined the repeatability of the R2R fabrication process when the active area of the module varied from 32.2 cm(2) to 96.5 cm(2). A thorough layer-by-layer optimization of the R2R printing processes resulted in realization of R2R-printed 96.5 cm(2) sized modules with a maximum power conversion efficiency of 2.1% (mean 1.8%) processed with high functionality.

The comparison of solution processed organic photovoltaics with two roll-to-roll coated electron transport layers (ETL), as well as printed grid or solid back electrodes provides insight into the future of R2R fabricated architectures. The variation in performance of the R2R slot-die coated zinc oxide (ZnO) versus the tin oxide (SnO 2 ), showed a clear dependence on the spectrum of the illumination source. It was found that under indoor light conditions (200-1000 lux LED and fluorescent sources) the SnO 2 outperformed the ZnO with highest efficiencies near 13% and 10% respectively. This is in contrast to results obtained under 1 Sun (AM 1.5) in which the cells fabricated with a ZnO ETL had a higher power conversion efficiency than those prepared with SnO 2 . The results also confirm the significance of the layout of the printed silver back contact; in which cells with the grid structure outperformed those with full coverage by approximately 35% for ZnO and just under 10% for SnO 2 (all light conditions). The combination of a R2R coating and S2S printing process to prepare modules with 8 cells in series (PET/ITO/SnO 2 /PV2001:PCBM/PEDOT:PSS/silver grid) resulted in a PCE of 13.4% under indoor office light conditions.