SUMMARY
[0005] The present invention aims to address all or at least some of the aforementioned deficiencies of the prior art. In particular it aims to provide efficient and robust low work function electrodes produced by commercially applicable deposition techniques, which provide for the production of organic photovoltaic systems by processes compatible with the requirements of large scale, high throughput mass production. These objectives are attained by the low work function electrode, the photovoltaic system, and the processes for the production of these as described in the following.
[0006] The present invention thus relates to a process for producing a low work function electrode for a photovoltaic system, which comprises depositing an electrode layer over a substrate. An ethoxylated polyethyleneimine (PEIE) layer is spray coated over the electrode layer. A low work function electrode for a photovoltaic system produced by this process is also within the scope of the present invention.
[0007] Moreover, the present invention is directed towards a process for producing a photovoltaic system, which comprises depositing a first electrode layer onto a substrate. An ethoxylated polyethyleneimine (PEIE) layer is spray coated onto the first electrode layer. A bulk heterojunction active layer is deposited onto the PEIE layer. A hole transport layer and/or a second electrode layer is deposited onto the bulk heterojunction active layer. A photovoltaic system produced by this process is also within the scope of the present invention. [0008] It is understood that the invention disclosed and described in this specification is not limited to just the aspects summarized in this Summary and can include additional aspects described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Some aspects of the systems and processes described in this specification can be better understood by reference to the accompanying figures, in which:
[0010] Figure 1 is a flowchart diagram illustrating a bottom up process for producing a photovoltaic system according to the present invention, wherein the order of the bottom up deposition steps reads from the top down in the diagram;
[0011] Figure 2 is a flowchart diagram illustrating a bottom up process for producing a photovoltaic system according to the present invention, wherein the order of the bottom up deposition steps reads from the top down in the diagram;
[0012] Figure 3 is a flowchart diagram illustrating a bottom up process for producing a photovoltaic system according to the present invention, wherein the order of the bottom up deposition steps reads from the top down in the diagram;
[0013] Figure 4 is a schematic diagram illustrating a photovoltaic system according to the present invention produced in accordance with the process illustrated in Figure 1 ;
[0014] Figure 5 is a schematic diagram illustrating a photovoltaic system according to the present invention produced in accordance with the process illustrated in Figure 2;
[0015] Figure 6 is a schematic diagram illustrating a photovoltaic system according to the present invention produced in accordance with the process illustrated in Figure 3; and
[0016] Figure 7 is a schematic diagram illustrating another photovoltaic system according to the present invention. [0017] The reader will appreciate the foregoing details, as well as others, upon considering the following detailed description of the processes and systems according to this specification.
DESCRIPTION
[0018] As described in this specification the present invention is directed to processes for producing low work function electrodes for organic photovoltaic systems, such as, for example, polymer-fullerene bulk heterojunction organic photovoltaic systems. The processes may comprise depositing an electrode layer onto a substrate and spray coating an ethoxylated polyethyleneimine (PEIE) layer onto the electrode layer. This multi-layer spray coating process avoids the functional surface area constraints imposed by other deposition techniques, such as spin coating, for example, and may be used to produce large-area organic photovoltaic systems with relatively high through-put.
[0019] As used in this specification, including the claims, the term "work function" refers to the minimum energy required to remove an electron from a solid material to a point immediately adjacent to the solid material surface. In the active material of an organic photovoltaic system, a photo-excited electron dissociated from its corresponding hole in the semiconducting polymer occupies the LUMO energy level of the acceptor material (e.g., a fullerene compound). Therefore, the work function of the cathode in an organic photovoltaic system must be sufficiently low in order to approximate the LUMO energy level of the acceptor material and
extract/collect the electron from the active material. On the other hand, the work function of the anode in an organic photovoltaic syste