Effect of different lead precursors on planar perovskite solar cells
Date of Issue2016
School of Materials Science and Engineering
Energy Research Institute @ NTU
Ever since emerging to the solar cell scene in 2009 as a light harvester in dye-sensitized solar cells, perovskite solar cells had progressed tremendously, reaching >22% within several years of intense study. However, much yet have to be understood scientifically in order to launch perovskite-based solar cells commercially. Charge transport mechanism with different selecting layers of perovskite solar cell is one such case. For this mechanism study, efficient planar solar cells with TiO2 and spiro-OMeTAD (n-i-p architecture), or PEDOT:PSS and PCBM (p-i-n architecture) as selection layer are required. Recent fabrication of perovskite solar cells using lead acetate precursor demonstrated the capability to obtain ultra-smooth and pinhole-free perovskite layer with short annealing time. In this research, process parameters to obtain good performance of inverted planar perovskite solar cells are thoroughly investigated. Subsequently, fabrication of solar cells with more optimal condition is studied under impedance analysis in comparison to optimal lead chloride-based solar cells. The results are as follows: 1. Uniformity of PEDOT:PSS layer is one of the important factors for high performance perovskite layer. Poor coverage of PEDOT:PSS leaves the bare ITO exposed to perovskite layer and becomes the recombination center. 2. The hydrate water inside the lead acetate precursor has no bad effect on the perovskite formation. 3. Increasing the spin coat speed (to 3000rpm for 30 seconds) can improve the uniformity of perovskite film and further current density of solar cells. 4. Film thickness can be adjusted by concentration of precursor solutions. 0.9M is the best currently. 5. Annealing at relatively low temperature (90oC) for 10 minutes produce the densest and pinhole-free perovskite film in morphology and performance compared to high temperature, like 100 oC. 6. Solar cell performance is strongly dependent on the perovskite film quality: large amount of holes inside the films acting as a charge recombination center reduces the open circuit voltage; too thin a film develops less current density; and the interface contact between PEDOT:PSS/perovskite/PCBM affect the fill factor of the whole device. All these parameters should be properly controlled to get high efficiency. 7. By this investigation, we could confirm reaching open circuit voltage of 0.9-1V and short circuit current density of 19 mA/cm2, similar to that of other research groups. 8. Upon impedance analysis, the recombination resistance of device from lead acetate is comparably lower to its optimal lead chloride-based counterpart. In addition, cell performance is seen to downgrade overtime and hysteresis is observed. Further optimization is still needed to achieve a highly efficient solar cell.
Final Year Project (FYP)
Nanyang Technological University