Composition Control Of Light Absorbing Layer Materials In Perovskite Solar Cells

Perovskite solar cells（PSCs）become a research focus for its excellent photovoltaic performance and simple fabrication procedure.In recent years,the power conversion efficiency（pce）of these devices exceed 20%,which becomes similar to CIGS solar cells and silicon solar cells.Although the device structures of PSCs were used by solid DSSCs and Polymer SCs formerly,the photovoltaic performance of PSCs are remarkable promoted,which should be contributed to the light absorption material of organic lead halides with perovskite crystal structure.Therefore,high quality perovskite layers are always desirable for fabricting high performance PSCs.In this paper,the high quality perovskite absorption layer was prepared by simple one-step spincoating with controlling the composition of the perovskite absorbing layer material,and the high efficiency perovskite solar cell was obtained.1.Perovskite solar cells can be fabricated by lead acetated based lead source,which can produce smooth and compact perovskite layers by simple one-step spincoating without the usage of anti-solvent.However,these devices exhibit poorer stability performance and efficiency for small grain size and grain boundary trap density.We introduce Pb（SCN）₂ as the additive of Pb（Ac）₂ precursor for preparing CH3NH3PbI3 light harvester layers of PSCs.It is found that Pb（SCN）₂ additive can encourage the growth of perovskite grains and promote the crystallization of perovskite layers.By optimizing the quantity of Pb（SCN）₂ additive,the PCEs of devices are improved from 14.0%to 17.2%.Further investigation indicates that Pb（SCN）₂additive can reduce the recombination process,which comes from the passivation of defect states at grain interfaces.And charge extraction process can also be improved by Pb（SCN）₂ additive.This strategy for precursor solutions can encourage the usage of non-halide lead source in the fabrication of perovskite devices.2.Compared with organic-inorganic halide perovskite,pure inorganic perovskite may have better long-term stability.The CsPb I₃ with a band gap of 1.73 eV is more suitable for the active layer of PSCs.And as reported,CsPbI₃ PSCs can be stable at room temperature and heating state.However,α-CsPb I₃ phase with photoelectric conversion ability is unstable at room temperature,and rapidly transforms to yellowδ-CsPb I₃ phase at room temperature.In order to obtain stableα-CsPbI₃ phase at room temperature,the grain size must be reduced as he surface strain produced by the small grain size is beneficial to the stabilization of theα-CsPbI₃ phase.However,small grains lead to excessive grain boundaries and defects in perovskite thin films,which are very unfavorable for device performance.We obtainα-CsPbI₃ at 155 ^oC by adding a small amount of 2D perovskite material EDAPb I₄ into CsPb I₃ perovskite precursor solution to improve the stability of theα-CsPbI₃.Meanwhile,a small amount of PCBM is added into the precursor solution to passivate the crystal defects and defects in perovskite films and improve the charge transfer capability of the devices.We improved the device performance by simple one-step spin coating and achieve the best PCE from 9.10%to11.3%.