All-solution processed regular organic solar cells using a new inkjet-printable cathode

The current developments in polymer organic solar cells are inspired by the idea that they can be processed entirely from solution. In all polymer cells the photoactive layer is processed from solution, most often the electrodes are not. Holst Centre has already developed a solution-processable anode, this project focusses on the development of a solution-processable cathode1 for solar cells with a "regular" configuration - that is, the cathode has to be processed on top of the other layers. To make a solution-processable cathode it is required to use high-workfunction metals which can be processed in the form of ink, like silver. When silver is used a cathode modification layer (Electron Transport Layer or ETL) is required. Out of several of materials for these layers that have been studied two were successful: zinc oxide (ZnO) processed from a nanoparticle dispersion in acetone and the polymer PFN which has been dissolved in ethanol. Solar cells with these ETLs and an evaporated silver cathode perform 12% lower than the reference design (with a LiF aluminum cathode). When comparing the reference design with an evaporated silver electrode without ETL the performance loss is 43%, thus the ETL significantly improves performance. The printing of silver on top of the ZnO layer was problematic because of crack formation. It was however shown that the principle worked, thus several methods were employed to prevent cracks. None gave reliable results. The layers were studied using AFM, conductive AFM, SEM and cross-sectional TEM. The printing of silver on top of PFN was successful: 35 out of 40 produced cells were working with the best performances reaching over 50% of the performance of the reference design. This success warranted the combination of the Holst anode with the new cathode to create all-solution processed devices with photovoltaic power conversion efficiencies reaching 1.95%.. - First prize Shell Bachelor Master 2012 "Organische zonnecellen : van lab tot fab". The current developments in polymer organic solar cells are inspired by the idea that they can be processed entirely from solution. In all polymer cells the photoactive layer is processed from solution, most often the electrodes are not. Holst Centre has already developed a solution-processable anode, this project focusses on the development of a solution-processable cathode1 for solar cells with a "regular" configuration - that is, the cathode has to be processed on top of the other layers. To make a solution-processable cathode it is required to use high-workfunction metals which can be processed in the form of ink, like silver. When silver is used a cathode modification layer (Electron Transport Layer or ETL) is required. Out of several of materials for these layers that have been studied two were successful: zinc oxide (ZnO) processed from a nanoparticle dispersion in acetone and the polymer PFN which has been dissolved in ethanol. Solar cells with these ETLs and an evaporated silver cathode perform 12% lower than the reference design (with a LiF aluminum cathode). When comparing the reference design with an evaporated silver electrode without ETL the performance loss is 43%, thus the ETL significantly improves performance. The printing of silver on top of the ZnO layer was problematic because of crack formation. It was however shown that the principle worked, thus several methods were employed to prevent cracks. None gave reliable results. The layers were studied using AFM, conductive AFM, SEM and cross-sectional TEM. The printing of silver on top of PFN was successful: 35 out of 40 produced cells were working with the best performances reaching over 50% of the performance of the reference design. This success warranted the combination of the Holst anode with the new cathode to create all-solution processed devices with photovoltaic power conversion efficiencies reaching 1.95%.. - First prize Shell Bachelor Master 2012 "Organische zonnecellen : van lab tot fab"