Study On Perovskite Film/Interface To The Stability Of Perovskite Solar Cells

Perovskite solar cells?PSCs?have achieved over 25%power conversion efficiency?PCE?,reaching one of the leading devices in new type of solar cells.However,compared with silicon solar cells,gallium arsenide solar cells,copper indium gallium selenium solar cells,etc.,stability issues prevent perovskite solar cells from commercialization.Toward stability,we should suppress defect states,thus improve the phase transition barrier by improving the film and interface quality of the perovskite.Besides,the interface passivation engineering can effectively suppress the erosion of perovskite by the attack of external polar molecules,which can not only reduce the defect states,but also protect the perovskite films in physics and chemistry.Focusing on the stability of perovskite solar cells,this paper has done the following work to improve the quality of perovskite film and interface:?1?Low-cost caprolactam?CPL?has been introduced into one-step anti-solvent process to fabricate efficient and stable planar PSCs for the first time.It is found that CPL as a Lewis base has the weak coordination ability to Pb?II?,and this weak interaction will be easily broken by either anti-solvent dripping or annealing owing to the steric effect,thus leading to a compact film with monolithic grains.Up to 19.2%PCE has been achieved.Especially,the PSCs exhibit superior stability in ambient condition,which PCE can be retained 95%of its initial PCE after 1200 hours.Further investigation suggests that the residual CPL in the perovskite film can well passivate perovskite grain boundaries and the interface by its interaction with Pb²⁺cations,thus leading to good anti-moisture and thermal stabilities of perovskite films.This work provides a new way to fabricate highly efficient,stable PSCs by adopting an appropriate Lewis base simultaneously for high quality perovskite films and passivation toward grain boundaries and interfaces.?2?Graphdiyne?GDY?has been introduced into the perovskite film to construct a perovskite/graphdiyne?PVSK/GDY?bulk hetero-junction for planar perovskite solar cells.This PVSK/GDY bulk hetero-junction is suggested to provide an extra channel to favor exciton separation and facilitate the photo-generated electron extraction ability.The electron transportation ability has been improved for higher J_sc,and the introduction of GDY can passivate grain boundaries and interfaces to effectively suppress photogenerated carrier recombination,leading to relatively higher fill factor.Up to 20.54%power conversion efficiency has been achieved.In addition,the ability of this perovskite film with PVSK/GDY bulk heterojunctions to function in humid conditions is also improved,leading to good stability of PSCs toward moisture.This work provides a new way to fabricate highly efficient,stable PSCs by constructing bulk heterojunctions simultaneously for accelerating the exciton separation and photogenerated electron transportation and improving the device stability.?3?Surface passivation is an effective approach to eliminate defect and thus to achieve efficient perovskite solar cells,while the stability of the passivation effect is a new concern for the device stability engineering.Herein,we introduce tribenzylphosphine oxide?TBPO?to stably passivate the perovskite surface.High efficiency of exceeding22%with steady-state efficiency of 21.6%has been achieved,which is among the highest performance of the Ti O₂ planar cells,and the hysteresis has been significantly suppressed.Further density functional theory?DFT?calculation reveals that TBPO intermolecular?-?conjugation induced surface molecule superstructure,such as periodic interconnected structure,has resulted in high stability of TBPO-perovskite coordination and passivation.The passivated cell has exhibited significantly improved stability,with sustaining 92%of initial efficiency after 250 h maximum-power-point tracking.Therefore,the construction of a stabilized surface passivation in this work represents a great progress in the stability engineering of the perovskite solar cell.?4?Quaternary ammonium salt is introduced to grow reduced-dimensional?R-D?perovskite structures in situ on the three-dimensional?3D?perovskite FAPb I₃ interface and grain boundaries.This structure passivates 3D perovskite interface and hinders electrons to move to the interface of the hole transport layer.Using this R-D perovskite interface passivation can greatly reduce defect states,thus improve the interface quality of perovskite.Finally,the passivated perovskite film carrier lifetime exceeded 10microseconds,and the reverse scanning PCE of the device reached 23.89%?steady-state efficiency 23.70%?.In addition,the water stability of perovskite films based on R-D perovskite interface has been greatly improved.And PCE can sustain 85%of initial efficiency after 200 h maximum-power-point tracking.