Research On Crystallization Regulation Of Light-Absorbing Layer And Photovoltaic Performance For Perovskite Solar Cells

Most recently, organic-inorganic hybrid perovskite solar cells (PSCs) have attracted extensive attention of the researchers due to their high efficiency, abundant source of raw materials and low-cost fabrication via solution process. Conventional PSCs employ MAPbX3 as the intrinsic light absorber, of which the crystallinity and morphology play crucial roles in affecting the photovoltaic properties. Preparing a high-qualifed perovskite film which may significantly improve the device performance could be realized by the modification effect of additives on the crystallinity and morphology. In this paper, benefiting from the particular role of adiitives in facilitating homogeneous nucleation and modifying kinetic processes of crystal growth, we have developed two different kinds of functional additives based on distinct regulation mechanisms. These functional additives are adopted to the light absorbers of multi-system planar heterojunction PSCs ameliorating the quality of perovskite film and consequently enhancing the device performance.To begin with, we prepare the light absorber in CH3NH3Pbl3-based planar heteroj unction PSCs with a two-step deposition method. The perovskite film is fabricated by firstly spin coated a PbI2 precursor solution with the addition of small organic molecular 4 tert-butyl pyridine, immediately followed by the immersion into a CH3NH3I bath. Taking the advantages of the strong interaction between Pb2+ and TBP molecules, we successfully prohibit the crystals from growing rapidly and a porous layer consisting of randomly oriented nanocrystalline is obtained. This method remarkably increase the interfacial contact area between solid and liquid phase facilitating the complete conversion to CH3NH3PbI3, which significantly ameliorating the crystallinity of CH3NH3PbI3 light absrober. Besides, porous structure in this perovskite film is observed which is conducive to the formation of p-n junction at the interface with hole transport materials. As a result, charge carrier transport is enhanced and eventually the power conversion efficiency (PCE) of this PSCs increase from 6.71% to 10.62%(enhanced 58%) with good reproducibility.Then, we apply TBP to CH3NH3PbI3-xClx-based PSCs. TBP acts as an additive to guide the orientational crystallization under the one-step deposition method. Consequently, a high-qualified perovskite film with superior light absorption and photon-to-electron conversion efficiency is obtained and the lower defect concentration efficiently suppresses the charge recombination resulting in a substantial increase in Voc and FF. As a consequence, the PCE increases from 11.11% to 15.01%(enhanced 35%).Finally, functional viscous polymer PEO (polyethylene oxide) is induced into CH3NH3PbI3-xClx-based PSCs. By the virtue of its stabilized framework, PEO makes a contribution to the construction of a network scaffold improving the crystallinity and film formation of perovskite. It turns out that a new-type cell configuration based on a network scaffold which consists of PEO framework material is developed. In such configuration, perovskite crystals are supported by the three-dimensional interpenetrating PEO network, which achieves a more controllable morphology and a more densed coverage on the substrate. Based on this strategy, a much higher Voc is attained and the maximum PCE up to 15.6% under standard AM1.5 illumination is highlighted. Moreover, these PSCs exhibits preferable long-term stability.