Chemical Stability Study Of Solar Cells Based On Novel Narrow-band Absorbers And Coping Strategies

Efficiency and stability of solar cells is the key to real life applications.Narrow-band semiconductors as absorbers in solar cells can effectively utilize the near-infrared light in solar spectrum to enhance efficiency.However,there are still some limits for current narrow-band semiconductors.Quantum dots?QDs?and organic-inorganic hybrid perovskites are two kinds of novel narrow-band semiconductors,with advantages such as solution process,high performance,low cost and so on.Based on these two kinds of novel narrow-band semiconductors as absorbers,this paper aim to study and solve the chemical stability of corresponding solar cells.For quantum dot sensitized solar cells,the open voltage is typically lower for polysulfide electrolytes than that for iodide electrolytes,but iodide electrolytes would degrade QDs quickly.Thereby we used inorganic halide ligands as modification layer to increase the stability toward iodide electrolytes.For perovskite solar cells,it was found that perovskite would be corroded easily by moisture,UV light,and heat.We aim to address the chemical stability of perovskite and underlying mechanism by interface modification and mixed cations.The main results and conclusions are as follows:?1?With iodide capping QDs,the stability of QDs in iodide electrolytes was significantly improved,while the charge transfer between TiO₂ and QDs,between QDs and electrolytes was also greatly enhanced,resulting in high open circuit voltage.The interaction mechanism of different halide ligands with CdSe and PbS QDs was also studied.In addition,electrophoretic deposition could be applied to fabricate QDs films,achieving higher adsorption amount than direct adsorption method,which was beneficial for short circuit current.?2?Through thermodynanmic calculations and experiments,we studied the degradation mechanism of perovskite in moisture atmosphere.Perovskite would combine with water molecue,and degrade to PbI₂,MA,and HI.The oxidation and photochemical reaction of HI forwarded the whole reaction.When a thin layer of Al₂O₃ was deposited onto perovskite,the degradation would be suppressed since the contact with moisture was cut off.Furthermore,the electron recombination was also suppressed after modification.?3?Compared to MAPbI₃,?MAPb I₃?_1-x?CsPbBr₃?_x perovskite films exhibited orientation along<112>/<200>directions rather than<110>/<002>directions,since CsPbBr₃ have different surface energy for each planes.In addition,the lattice parameters decreased for the mixed perovskite,protecting perovskite from degradation by moisture,while Cs atoms could decrease the decomposition of MA under UV light illuminations.?4?We studied the degradation process under thermal treatment,since oxygen could oxidize MA.For Cs_xMA_1-xPb I₃ perovskite,the oxidation of A site atoms could be suppressed,leading to better thermal stability.Moreover,Cs atoms could decrease the trap density,and increase the film thickness,leading to better efficiency.