The Study Of Heterojunction Perovskite Solar Cells

Organic/inorganic hybrid perovskite solar cells have been becoming a new hotspot in the field of solar cell community. The efficiency of this new generation solar cell has risen to more than 20%, which is close to the PCE of monocrystalline silicon cells. In addition, both the raw material of low cost and simple preparation technology show a promising application potential. However, this exciting device is still in re-search stage at present stage. Based on the main perovskite materials such as methyla-mine lead iodine and formamidine lead iodine (MAPbI3 and FAPbI3) the solar cells fabrication process and structural optimization still need to be investigation to further enhance its performance.Bas.ed on the above-mentioned considerations, this paper studied the effect of perovskite precursors, solvent system and low temperature processed titanium dioxide (TiO2) nanoparticles on the performance of the perovskite solar cells. Details are pre-sented as follows:(1)Although FAPbI3 perovskite has a lot of obvious advantages in spectral ab-sorption and thermal stability, its harsh synthetic condition has been one of the factors that limits its development. This paper firstly synthesized hydroxyl iodine lead (Pb(OH)I) to replace the traditional lead chloride (PbCl2) and lead iodide (PbI2). By using one step solution method to synthesis FAPbI3, under low temperature (150℃) it is easy to form the space group for P63mc yellow crystal. When heated to 160℃ it got perovskite crystal FAPbI3. The crystal space group of FAPbI3 is P3ml, The band gap of FAPbI3 is 1.475 eV in this study and absorption edge can be up to 820 nm. However, due to the low coverage of FAPbI3 film (less than 90%) which leads to the photoelec-tric conversion efficiency (PCE) is only 6.1%.(2) One efficient way to improve the device PCE is to improve uniformity of the perovskite film. Additive approach, such as CH3NH3Cl or NH4Cl, was usually intro-duced into the precursor solution. In this paper, we found that, based on MAPbI3, add-ing certain amount of DMSO into the DMF solvent, could also achieve the goal of im-proving morphology uniformity. Along with the increase in the amount of DMSO, the uniformity of the film was increased, but when the molar ratio of DMSO to Pb is ex-ceeded 1 in the precursor solution, the uniformity of the film decreased again with low film coverage. The optimized mole ratio of MAI:Pbl2:DMSO is 1:1:1. It was sup-posed that the DMSO and DMF coordination effect is beneficial to reduce the crystal-lization of the intermediate phase and suquentially- improve the smoothness of the fi-nal perovskite film. With the mixed solvent approach, the efficiency of the mesoporous MAPbI3 film solar cells reached 11.2%.(3) We further employed TiO2 nanoparticles layer to replace the traditional com-pact/mesoporous TiO2 layers and realize low-temperature preparation of perovskite solar cells. Spinning the TiO2 nanoparticles from the TiO2 nanoparticles aqueous dis-persion on FTO substrates directly and dried at 150℃ for 30 min, then spinning per-ovskite and HTL, and finaly evaporating the Ag electrode to complete the device with an efficiency of 14.3%.