Comparison of the solution and vacuum-processed quinacridones in homojunction photovoltaics

Abstract: In this work, we explored industrially relevant pigments quinacridones as organic semiconductors with respect to their applicability in air-stable homojunction (single material-single layer) organic photovoltaic cells. We studied quinacridone and two linear transquinacridones, i.e., Pigment Red 122 (2,9′-dimethylquinacridone) and Pigment Red 202 (2,9′-dichloroquinacridone) in vacuum-processible OPV films and compared their performance to OPV films made from their solution-processed counterparts. We show that this class of materials generates photocurrent without the need of creating a donor–acceptor junction. Stable homojunctions were created both via vacuum-processible and solution-processible routes, with the latter method based on the chemical functionalization of the respective molecules with the thermolabile group, t-BOC, that affords solubility in various organic solvents and conversion back to the parent molecule via exposure to temperatures around 170 °C for periods not exceeding 30 min. We show that power conversion efficiencies around 0.15% are reachable without scrupulous optimization of the homojunction cells in terms of electrode surface functionalization or film deposition conditions. This class of materials holds promise for the further development of a new generation of air-stable organic photovoltaic cells based on simple fabrication technologies. Graphical abstract: [Figure not available: see fulltext.]