Hole Interface Property Optimization In Hybrid Perovskite Solar Cells

The past decade has witnessed the rapid development of organic-inorganic metal halide perovskite solar cells（PSCs）,whose power conversion efficiency（PCE）has increased from3.8%to 25.7%.Contributing from the excellent optoelectronic properties of lead-halide perovskite material,such as low exciton binding energy,high optical absorption coefficient,tunable band gap,and long carrier diffusion length,it has become a research hotspot in the field of materials for solar energy application.At present,there still exist some dominating problems that are limiting the further breakthroughs in efficiency and commercialization of PSCs,such as defects in perovskite bulk phase and interfaces,mismatch of interfacial energy levels,low carrier extraction rate,and poor device stability.In this thesis,we apply interface engineering strategy to enhance hole extraction and transport in the hole transport layer,and suppress nonradiative recombination via modifiing perovskite surface and passivating defects.The thesis includes the following two parts:（1）A small-molecule heterocyclic multifunctional organic salt（1H-pyrazole-1-formamidine hydrochloride（PAH））is utilized to modify the surface of the formamidine based perovskite.Firstly,a series of characterizations are conducted to verify the strong interaction between PAH and Pb²⁺at grain boundaries under mild conditions.Meanwhile,the morphological characterization results demonstrate that PAH will anchor to the stacking interfaces of perovskite crystals,and the excess lead iodide on the surface is effectively passivated.With PAH induced secondary growth,the size of perovskite crystals increases to form a more uniform perovskite film.Moreover,the study of charge carrier dynamics indicates the elevation of charge extraction and transport rates,which can be attributed to the matched alignment of energy levels after PAH modification.Benefiting from the defect passivation effect via PAH modification to suppress charge recombination and enhance charge transport,an improved short-circuit current(J_sc),open circuit voltage(V_oc)and fill factor（FF）are obtained.The PCE of the device increased from 17.38%to 20.90%,and the hysteresis is also significantly suppressed.（2）Nickel oxide is a commonly used inorganic hole transport material in inverted perovskite solar cells,however,its drawbacks still remain to be solved,such as vacancy defects,lattice mismatch with perovskite and poor hole extraction ability.In this work,graphdiyne（GDYO）is doped into nickel oxide to prepare an efficient composite hole transport layer.Graphdiyne is a new carbon material with independent intellectual property rights in China,exhibiting excellent semiconductor and charge transport properties.As a functionalized graphdiyne,GDYO possesses oxygen-contained active groups（hydroxyl,carboxyl,etc.）to efficiently fill the oxygen vacancies at the interface of nickel oxide.With the introduction of GDYO,the nickel oxide film becomes smoother with obviously reduced roughness.Moreover,the hole mobility of the GDYO involved composite film is significantly improved.Compared with the reference device 16.93%,the PCE of the perovskite solar cell increased to 19.1%,and the device FF was significantly improved（80.94%）.