Intellectual Property

Individual conventional solar cells have limited spectral coverage, voltage output, and tradeoff between absorption length and charge collection length. By stacking multiple solar cells with complementary absorption profiles, voltages of the cells can be added (at a constant current).

In order to prepare solar cells with efficiencies higher than theoretical limits, researchers have turned to multi-junction cells, however, these cells are very expensive. An alternate approach is to collect the high energy part of the spectrum, and double the energy collected from this part of the solar spectrum using singlet fission materials which absorb high energy light and generate two excitons for every photon absorbed, thus doubling the light collection efficiency. This approach has the potential to give a single solar cell a 45% efficiency, without increasing the cost to produce the cell.

Fullerenes include molecules such as C60, C70, C84 and derivatives that are designed to dissolve in solvents (such as PCBM made with either C60 or C70). Fullerenes are the most prevalent acceptor in organic photovoltaics and offer better efficiency than any other acceptor molecule to date.

In planar cells the thickness of a layer is limited by the distance an exciton is expected to travel before it recombines. If the layer is too thick, photons absorbed may never result in collected charge. If the layers are too thin, there is insufficient material available for absorption of the light. By mixing the donor and acceptor throughout a thicker layer, an additional donor-acceptor interface is created throughout the layer, improving photocurrent generation capability.

In most solar cell designs, excitons must be blocked and reflected away from the metallic (or transparent) contact so that they can be dissociated at the donor-acceptor junction. Additionally, it is desired that these layers block the wrong carrier from contacting the electrode.

In certain applications it may be desirable to have a partially transparent solar cell. These applications include tinted windows. Instead of just absorbing or reflecting the light, the light would be absorbed and converted into energy. The unique nature of organics allows NanoFlex to tune the wavelengths absorbed to those not useful for vision, such as in the infrared region of the spectrum.

Current OPV materials absorb light in the visible and deep red part of the solar spectrum, but do not collect light in the near infrared (NIR). Extending efficient light collection into the NIR has the potential to increase photocurrent generation by 40%, markedly improving OPV performance.

One of the most air sensitive parts of the OPV is the region between the anode and electron acceptor. This region is degraded by oxygen and water in the dark and even more so under illumination. If the OPV is prepared as an inverted cell, the air sensitive region is placed below the donor, buffer layer and cathode. Thus, the device itself provides a level of "packaging," markedly slowing environmental degradation of the device, minimizing packaging requirements for long term deployment in the field.

A number of growth technologies have been developed for organic materials. These include vacuum thermal evaporation and organic vapor phase deposition for materials that can be sublimed or evaporated directly and gravure or ink-jet printing of dissolved materials. All of these processes are compatible with rigid planar substrates, but more importantly can be applied to flexible plastic or metal foil substrates, for roll-to-roll fabrication of OPVs.