A Solution Processed Carbon Electrode for High Volume Roll-to-Roll Manufacture of Flexible Perovskite Solar Cells

Recent experiments involving a new carbon electrode demonstrate a true fully roll to roll coated perovskite solar cell via a continous slot die coating method. All previous reports of roll to roll coated perovskite solar cells have completed the device off-line with an evaporated metal contact. The application of a wet carbon film continuously and compatibly with an underlying perovskite device stack in a moving web at manufacturing speeds is complex but game-changing. The ability to sequentially deposit all layers of the device stack culminating in a fully working device entirely in-line means that the promise of high volume “liquid in/solar cell out” can be realised.<br/><br/>This multifunctional carbon electrode can be safely deposited on top of a layered solar cell without any deformation or dissolution of the underlying layers. The new contact material overcomes issues of solvent incompatibility, interface incompatibility and narrow rheology and heating process windows.<br/><br/>In this talk we will present the development journey of this new electrode material and the recent succesful pilot run of the material. In particular we will show how we formulate a new carbon ink with solvent compatible with the perovskite stack that crucially has suitable boiling point for low temperature, high speed processing coupled with very low toxicity (no work place exposure limit). The solid loading of the ink is optimised for a rheological profile suitable for slot die and we demonstrate the roll to roll slot die coating of the electrode sequentially following the roll to roll coating of the NIP device stack incorporating a low temperature processed p type interlayer. The carbon ink is formulated with solvent system orthogonal with the device stack and with no detrimental action on the perovskite active layer as shown through X-ray diffraction analysis. Electrochemical impedance spectroscopy and steady state photoluminescence analysis reveal that charge transfer at the interface is equivalent to evaporated gold electrodes. Further, the device stack is demonstrated to have no detrimental effect on stability, unencapsulated cells retained 90% of original PCE at atmospheric temperature for 1000 hours and outperform gold electrode cells at elevated temperature.<br/><br/>This work introduces the very first entirely roll to roll devices achieving efficiency matching evaporated gold electrodes. This first fully roll-to-roll coated perovskite prototype promises the possibility of transferring to industrially efficient PV production in the near future.