24 - 28 October 2016 • Marina Bay Sands Sands Expo and Convention Centre, Singapore
We investigated the origin of hysteresis in I-V curves of a planar perovskite cell using different equivalent circuit models. A planar cells showing huge hysteresis with PCE 18.0% on reverse scan and 8.8% on forward scan was used for validating the equivalent circuits. We found that the equivalent circuit model composed of two series connected diodes, two capacitors, two shunt resistances and a series resistance clearly reproduced the hysteretic I-V curves. According to this equivalent circuit model, the computationally simulated I-V curves matched closely with the experimental one. This suggests that perovskite cell has two active interfaces; TiO2/CH3NH3PbI3 and CH3NH3PbI3/spiro-OMeTAD. Hysteresis is essentially caused by carrier accumulation at these active interfaces. The electrical capacitances generated by defects due to the lattice mismatch at the TiO2/CH3NH3PbI3 and CH3NH3PbI3/spiro-OMeTAD interface are truly responsible for the hysteresis in the perovskite solar cells.
Based on above experience and knowledge, we also examined to evaluate the cell performance at low light intensity condition. Very surprisingly, due to the charge / discharge property with internal capacitance, we found the limitation to define the cell performance from the I-V curve because of the fake current. To solve this issue, we newly propose the Maximum Power Point Tracking (MPPT) technique to define the most accurate cell performance of the hysteric device.
Prof. Satoshi Uchida is professor in Komaba organization for educational excellence college of arts and sciences (KOMEX), The University of Tokyo. He received his PhD from Tohoku University in 1995 and moved to current status in 2006. His research focuses on the field of dye-sensitized solar cells (DSSCs), specifically cell assembling technique such as full-plastic, light-weight, film type as a ubiquitous power source. He is now also showing activity of Perovskite Solar Cells based on the crystallography, surface engineering and electronic simulation.