Organic photovoltaic (OPV) technology has been rapidly growing in performance and popularity over the past few years and is expected to become a major PV technology within the next decade. Here’s why.
In 2007, U.S. energy consumption surpassed 4 TWh per year, more than 25% of the world’s energy demand. More than 70% of this energy was derived from foreign non-renewable sources, making the need for renewable sources of energy increasingly urgent. The next generation of sustainable energy technologies will revolve around transformational new materials and technologies that convert practically infinite energy sources, e.g., sunlight and nuclear reactions, into electrical power.
Sunlight is the largest carbon-neutral energy source, with 89 petawatthours of sunlight reaching the earth’s surface, or almost 6,000x more than the 15 TWh consumed by humans. Solar electric generation also has the highest power density (global mean of 170 W/m2) among renewable energies. As can be seen in Figure 1, it would take only a relatively small percentage of the earth’s surface area — less than 5% — covered with only moderately efficient solar panels to more than meet energy needs worldwide. Moreover, the demand for such renewable energy sources is growing — projected over $100 billion in China alone by 2025 — and will represent a substantial market for capable manufacturers. Currently, however, only a small fraction of the world’s energy needs are generated by solar technologies. This huge gap between present solar energy production and its enormous potential is due to a number of factors, with manufacturing costs being one of the key barriers.
Thin film photovoltaic technologies offer a means to reduce these manufacturing costs by using smaller materials quantities and unique high-throughput manufacturing processes; however, many contain toxic or non-earth-abundant elements and progress in moving from laboratory to module efficiencies has been slow despite heavy investment. In contrast, thin-film OPV technology retains the benefits of other thin-film technologies but uses low cost, nontoxic, earth-abundant materials and offers the tailorability, manufacturability, flexibility, and light weight of modern plastics.
Comparison of Competing Technologies
The high capital cost of conventional PV systems is the primary reason that, after more than 50 years of development, the contribution of solar energy to global power generation remains at <0.5%. Reducing production cost is absolutely critical for broader market acceptance. Thin film technologies, including a-Si, cadmium telluride (CdTe), copper indium (gallium) diselenide (CIGS, CIS), dye-sensitized solar cells (DSSC), and organic (bulk heterojunction) photovoltaic (BHJ OPV) cells offer the potential for reduced capital costs through the use of smaller materials quantities and unique high throughput manufacturing pro cess es. Each PV technology has advantages and disadvantages, but only OPV offers the unique, transformative combination of low cost, mechanical flexibility, light weight, low-light performance, and optical transparency using materials.
Organic semiconductors are composed of inexpensive, earth-abundant, non-toxic, light elements, and have high optical absorptivity that reduces the need for thick photoactive films, all resulting in reduced module weight and leading to lower transportation and installation costs, along with less disposal waste. These materials can be easily formulated into inks, enabling extremely inexpensive solar cell production over large areas by high-throughput, roll-to-roll printing. Furthermore, all processes are performed at far lower temperatures than silicon (Si), thus dramatically reducing production energy costs and enabling fabrication on inexpensive substrates. Although the theoretical maximum power conversion efficiency (PCE) of OPVs is lower than for inorganic PVs (~ 20% vs 30%), once module efficiencies can achieve 10% or greater, the industry will shift to OPV technology because of the significantly lower-cost of production and installation. These factors will guarantee large-scale energy production at costs far lower than current Si. Moreover, OPV efficiencies have been increasing rapidly, moving from ~3% to Mitsubishi Chemical’s recent announcement of a 10%+ OPV cell in just a few years.
OPVs also exhibit better low-light performance than all other PV technologies, increasing overall output, which effectively increases efficiency beyond its rated value. Additionally, OPVs can be produced in a semi-transparent format and manufactured at high speed for encapsulation in low-cost glass or plastic. The power-producing glass can be used for new construction, replacement windows, atriums, skylights, and greenhouses, and with a power-to-weight ratio more than 3x that of CIGS, OPVs can be more readily integrated into electronics, consumer products, and even clothing, making it a truly transformative and sustainable energy technology.
The technology itself is also quite “green”: OPVs have by far the lowest energy use for the manufacturing of models (MJ/Wp), along with the lowest CO2 footprint (g CO2/Wp). The overall energy payback time (i.e. how long until a module has produced as much energy as went into producing it) is only about 2.5 months, and the capital expenditures required to build an OPV manufacturing plant are extremely small relative to other PV technologies. Consider that the cost of building a 1 gigawatt c-Si fab is approximately $2 billion; for OPV, the cost is about $200 million, or about one tenth the cost.