Research On Solution Processed And Annealing Free Transport Layer In Polymer Photovoltaic Cells

Recently some of the most attacting and practical ways to improving the PCE of organic solar cells consist of synthesizing narrow bandgap active layer materials, incorporating light-trapping structures, modifying the interfaces and so on. WO3 and MoO3 have a relatively high melting point, 795℃ and 1473℃, respectively. Thus it costs much more money and time when functioning as hole transport layer through high-vacuum evaporation method. So it is necessary to search for materials with low melting point which is suitable for acting as transport layers. As for PEDOT:PSS and TiO2, in order to improve the quality of the transport layer film, an annealing process is needed after spin coating. In addition to making the fabricating process more complex, the annealing process will cause a second time damage to the active layer when the structure of the solar cell is invented. As a result, spin coating method without annealing process is beneficial to fabricating organic solar cells.P type semiconductor material CuI was selected to function as hole transport layer in organic solar cell through high-vacuum evaporation method. The structure is shown as ITO/PEI/P3HT:ICBA/CuI/Au. PEI was dessolved into deionized water with a concentration of 0.2mg/ml to act as the electron transfer layer through spin coating method. The melting point of CuI is 600℃, thus the evaporation current was one third of that of the WO3. It lowered the costs of the fabricating process. On the other hand, the valence band energy and conduction band energy are-5.1eV and-2.1eV respectively, which match the energy levels of P3HT:ICBA and Au. The absorption edge of PMA is around 400 nm, so no absorption competition will occur between CuI and active layer. Results proved that devices with 2nm CuI achieved the optimal performance. The PCE is 1.6 times higher than that of devices without CuI.P type semiconductor material PMA was dessolved into isopropyl alcohol and span coated on the surface of active layer to act as the hole transport layer. The valence band energy and conduction band energy are-4.73 eV and-1.73 e V respectively, which match the energy levels of PCDTBT:PC70BM and Ag. The absorption edge of PMA is at 416 nm, so it will not compete with active layer about light absorption. The saturated vapor pressure of isopropyl alcohol is very high, thus the isopropyl alcohol evaporates fast once the PMA solution is spun coated on active layer. The feature eliminates the annealing process. PMA solution with a concentration of 2.5mg/ml was spun at a speed of 4000r/min, and the device achieved an optimal PCE of 6.57%, which is comparable wth that of devices using MoO3 as the hole transport layer through high-vacuum evaporation method. On account of the annealing-free procedure, the experiment cost is eventually reduced.