Low cost organic structures for high efficiency perovskite based solar cells

• Main Author: Desai Virali Jatin
• Other Authors: Subodh Gautam Mhaisalkar
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Materials::Energy materials
• Online Access: http://hdl.handle.net/10356/61149
• Institution: Nanyang Technological University

This project aims to provide a comprehensive study to incorporate inexpensive, easy to synthesize, organic nanomaterials as a scaffold for CH3NH3PbI3 perovskite loading and as a hole transporting material in the solar cells. In the first part of the project, electrospinning technique was employed to synthesize a scaffold to replace the TiO2 mesoporous layer and in the second part, an alternative chemical composition for the hole transporting material was characterised. The photoexcited electrons have high chance of recombination when they pass through the TiO2 film which lowers the performance of the perovskite solar cells. The creation of an insulating scaffold aims to lower the recombination process, increase the dye percolation and improve the charge transport and collection in photoanode of perovskite sensitized solar cells. The scaffold was created using electrospinning method. The process parameters such as type of polymer, applied voltage, feed rate were varied to obtain the optimum conditions to create nanofibers. Polystyrene scaffold made at 28kV with feed rate of 2mL/h showed large bead like formation that is not desirable as a scaffold in the perovskite solar cells. Polyvinylidene Fluoride scaffold was made by dissolving17 wt% of PVDF powder in 50wt%-50wt% of dimethylacetamide(DMA)-acetone solvent at the optimum process parameters of 20kV and feed rate of 0.5 mL/h. This resulted in uniform and elongated nanofibers with diameter of 440nm. The synthesized PVDF scaffold was sensitized by CH3NH3PbI3 perovskite using the single step approach. Sequential depositions of perovskite lead to the nanofibers being dissolved in dimethylforamide (DMF) solvent. The cells displayed good Voc values of 0.9 but a low efficiency. The main reason for contributing to the low fill factor and low current densities is attributed to the very thick nanofibrous film which enhanced the series resistance of the film dramatically thereby leading to poor charge collection. The electrospinning parameters need to be further optimised to obtain nanofibers of smaller diameters in order to achieve lower thickness of the scaffold. In the second part of this project, the effect of 2 new organic hole transporting materials (HTMs), namely T102 and T103, was investigated in the perovskite based solar cell. They exhibited a high efficiency of 12.2 %and 12.34 %. The fill factor of T102 was found to be very high, i.e 0.69 whereas fill factor of T103 was relatively lower, i.e 0.62. Impedance spectroscopy was done to analyse the origin for the difference in FF values. The impedance spectroscopy revealed that high fill factors for T102 are achieved due to the low series resistance of HTM layer whereas low fill factors for T103 are obtained due to high series resistance. The difference in the series resistance occurs due to the coverage of the htm on the perovskite layer. If the htm solubility in the solvent is good and if it conforms smoothly on the perovskite, the collection of charge (hole) is facilitated easily which is reflected as lower series resistance. The perovskite solar cells constructed with these newly synthesised HTMs have a good performance and has a potential to replace Spiro-OMeTAD for reducing the cost of these cells significantly.