**4. Industrial concerns**

performance has not yet been well studied. There are research attempts to incorporate various non-solvent additives, such as nanoparticles [126], carbon nanotubes [127], small molecules [128] and polymers [129], to create a ternary blend BHJ solar cell. These strategies have demonstrated how a third component in the polymer/fullerene blend influences the overall morphology and performance of the solar cell, which could be used as a potent routine method

**Figure 7.** Summary of parameters that influence the morphology of the BHJ active thin film.

Thermal annealing is an alternative method for controlling the BHJ morphology and improv‐ ing the PCEs. By applying thermal energy to the thin film, it helps the reorganization of the polymer/fullerene blends and increases the crystallinity of the film [131]. This processing method has been routinely used to optimize the thin films for transistors [132] and BHJ solar cells [20,21]. The annealing temperature, the annealing duration and the cooling rate are key parameters to optimize the performance of the device and the optimal combination of the thermal treatment is material-dependent. Even for the same material, e.g., P3HT/PCBM blend, the optimal annealing condition differs from lab to lab [20], presumably due to different device structure, different solvent, different purity, different molecular weight, or even different operator. So far there is no general guideline to predict the optimal condition for a new OPV

material and the optimal condition is obtained via a tedious trial-and-error approach.

to enhance the performance of the device [130].

370 Solar Cells - New Approaches and Reviews

As the ultimate goal of any material related research and technology development is to apply the material and to fulfill the promises of the material, such stress on the large scale manufac‐ turing and product development has also been witnessed for OPV technology. With the fast performance improvement of OPV cells in research labs, the application of OPV technology as a renewable energy source has become more appealing. However, it is never trivial to translate a lab-based technology into a large volume production process. A large number of difficulties and problems have to be overcome to ensure the successful commercialization of the technology. In this session, we will highlight some aspects related to the industrialization of OPV technology.
