Organic photovoltaics or dye sensitised solar cells - which will win? - SolarStar

 Organic photovoltaics (OPV  s) and dye-sensitised solar  cells (DSSC) together form the third generation of photovoltaic devices. They both promise low-cost and flexible solar cells  fabricated using roll-to-roll techniques. They both have target markets which significantly overlap. They therefore offer investors and customers similar value propositions.

In this short article, we critically compare and contrast OPVs and DSSCs in an attempt to identify the winners. We will base our assessment both on the state of the technology and the market.

From a technology point of view

OPVs and DSSCs operate on very different physical mechanisms. The former uses organic semiconductors to covert light to electricity, while the latter works very much like a photosynthesis process in which dyes generate the photo-excited charges. In spite of this stark difference, their macro attributes are strikingly similar. They both have low efficiency values (only a few percentages for the best production cells), a range of different degradation mechanisms limiting their lifetime, unfavourable cost structures, etc. It is therefore difficult to separate the two technologies purely on the basis of their technical performance.

Going forward, it is also difficult to assess what will come to separate the two. The range of organic chemistries that can produce suitable semiconductors is diverse, but recent progress has been incremental at best. Similarly, there are several dye formulations and electrolyte structures that can be used in DSSC devices. Here too however, despite years of research, efficiency progress has virtually stalled. Today, DSSC devices being commercialised across the industry use similar material sets and device architectures.

Another critical technology is the barrier layer required for extending device lifetime. While these two PV technologies suffer from different degradation mechanisms, they both demand high-performance barriers in order to insulate them from the external environment (e.g., in-diffusion of oxygen and water species will damage both devices). In both cases, different approaches are being followed to realise a suitable barrier layer, but in neither case does a barrier technology with a favourable cost-performance point exist.

The transparent conductor is also a major cost driver in both cases. Here, innovation in terms of replacing ITO is likely to equally benefit both PV technologies, which means that it will not be distinguishing factor.

From a market point of view

Both technologies are likely to fail in penetrating the utility market. This is because they are an expensive option, both in terms of dollars per watt and sustained return on investment (i.e., lifetimes are limited). This is particularly true at a time when the price of other PV technologies, i.e., crystalline silicon, is tumbling.

Indeed, we assess that both technologies will have limited uptake in all outdoor markets unless a seasonal design factor/product is involved. Our negative assessment extends to applications where solar cells are coupled to building/structural materials such as steel. The main value proposition here is low-weight compared to other PV technologies, but we assess that lifetime constrains rule these markets out.

In contrast, the competition will be intense in indoor applications between OPVs and DSSCs. This is because both technologies perform better than other thin film PVs under fluorescent lamps, which is predominantly used in retail environments.

Recent reports indicate that DSSCs outperform OPVs under fluorescent light, but our assessment is that a one-to-one comparison is difficult. This is because DSSCs and OPV refer to a class of PV technologies and not a single device type with a fixed material set and/or design. Therefore, comparisons will have to specify which DSSC was benchmarked against which OPV. Today, there is no comprehensive benchmarking study.

DSSCs outperform amorphous silicon under fluorescent lighting conditions. Source: Solarprint

Both OPVs and DSSCs offer good design factors such as semi-transparency and flexibility, which can be an advantage for indoor products demanding high aesthetics. These factors, together with the good indoor performance, indicate a competitive advantage in indoor applications.

But the story does not end here. In contrast to outdoor applications, a solar cell is not an end product in indoor applications. This is because it will have to be incorporated as a component into other products such as mouse pads, remote controls, keyboards, curtains, lampshades, light or temperature controllers, bags, self-powered sensors, etc.

This suggests that companies will have to constantly innovate and design products. In addition, they will have to partners with other companies to sell their panels as add-ons. Therefore, we assess that the winners will not be the ones with the best technology, but the ones offering the best portfolio of innovative products and/or having the best links with manufactures/distributors of consumer products.

The challenges however do not stop at the innovation hurdle. There are also fundamental business barriers. One is that customers will be expected to pay dearly for the energy produced using DSSCs or OPVs which are incorporated into their products. In fact, our estimates show that this energy will be orders of magnitude more expensive than that achievable using other PV technologies. Also critically, simple coil cell batteries offer adequate and even elegant solutions in many cases.

More critically however, DSSC or OPV manufactures have to achieve sales on the order of tens of millions of units to generate a ten million dollar profit. This holds true even when assuming that manufactures succeed in premium pricing the generated energy at >20 $/W. Achieving this level of sales will be a challenge, particularly because other options on the market offer better prices and performance levels.

In conclusion, we assess that little separates DSSCs and OPVs from the market or technological point of view. Here, the winner will be company that succeeds in designing the highest number of innovative products for indoor retail environments, regardless of the underlying technology. Even in this case, serious questions remain since large numbers of products must be sold in order achieve reasonable profits. Hitting these targets would have been a challenge for any product, but it is even more of a task given the constraints of DSSCs and OPVs such as low efficiency and limited lifetime, and given its competition.