Study On Small Molecular Biomaterials For Perovskite Solar Cells

Due to the advantages of high carrier mobility,wide light absorption range and low-cost preparation,perovskite solar cells(PSCs)display great promise in next generation photovoltaic technology.After more than ten years of development,the certificated power conversion efficiency(PCE)of PSCs have reached to 25.5%.On account of the low-temperature preparability and negligible hysteresis,the inverted structure PSCs have attracted extensive attention.However,the inverted PSCs still face many problems.As a common electronon transport layer(ETL),the carrier mobility of[6,6]-phenyl-C₆₁-isobutyrate(PC₆₁BM)can satisfy the needs of high-efficiency PSCs,but the cost problem is prominent due to the complex synthesis process.At the same time,PC₆₁BM tends to aggregate at high annealing temperature and sensitive to water and oxygen,which is bad to the device stability.Meanwhile,the inverted structure PSCs based on nickel(x)oxide(NiO_x)as hole transport layer(HTL)always presents low fill factor(FF)and open circuit voltage(V_oc)due to the high trap density of the NiO_x film.In addition,defects at the grain boundary and the long-term stability of devices are still the main challenges for PSCs commercialization.In view of the above problems,relying on the unique advantages of natural biomaterials in environment-benign,low cost,and diversity,this thesis focuses on the application of biomaterials in the inverted PSCs to realize the optimization of key layers,so as to improve the device photoelectric performance and stability.The specific work is as follows:(1)Coenzyme Q10 was used as an effective non-fullerene ETL in inverted PSCs.After systematically studies on energy level,carrier transport and kinetics,it was found that coenzyme Q10 was suitable for ETL.Because of the unique quinone group,coenzyme Q10 showed good electron transport ability.Meanwhile,coenzyme Q10 can reduce the defects at ETL/perovskite interface,thus inhibite the non-radiative recombination of carriers.Charge density difference calculations also confirmed that coenzyme Q10 exhibited more effcient charge transport ability than PC₆₁BM.The device based on coenzyme Q10 as ETL yeiled a PCE of 14.34%,which was comparable to the control device of 16.30%.Moreover,Q10 molecular with a long alkly chain gifts great hydrophobic property.Under the ambient condition of 30 ^oC,25%relatively humidity,the unencapsulated Q10 device showed better stability.(2)Adenine was used as surface modifer on NiO_x substrate for the energy level modulation.After adenine modification,the hole transport ability of NiO_x improve significantly.Simultaneously,the surface defects of NiO_x were passivated,so as to reduce the non-radiative recombination of carriers.The energy level of NiO_x was adjusted to better match that of perovskite,thus improve the V_oc.Moreover,a larger grain size and higher crystallinity of perovskite film was achieved on the adenine modified substrate.It was confirmed that the crystal structure of perovskite was more stable on NiO_x/adenine substrate by the density functional theory(DFT)calculations.These benefits enabled a higher V_ocand J_sc in the corresponding adenine modified devices with PCE increased from16.76%to 18.96%.When kept at room temperature and 50?60%relative humidity after600h,the unencapsulated adenine modified device maintained 90%of its initial PCE.(3)The effect of 5-(ethhiyl)-1h tetrazolium(ETT)on the properties of methylammonium lead triiodide(MAPb I₃)perovskite was investigated.Because of the interaction of lone pair electrons in tetrazole with Pb²⁺,the surface defects of perovskite films were passivated,thus leading to the inhibition of carrier recombination.Meanwhile,the introduction of ETT improved the crystallinity of perovskite film,and the average grain size had incearsed by 1.59 times.Combined with a series of carrier dynamics tests,it was proved that the carrier transportation was faster and the extraction was more effective for the device after ETT modification.The improved crystallinity and defect passivation enabled a PCE of 20.49%in the ETT-modified device,along with notably enhanced UV and moisture stability.(4)The defects passivation of perovskite with a fluorinated oligomer(FO-19)was investigated.The perovskite film was doped with the resin monomer 4,4-bis(4-hydroxyphenyl)valeric acid(DPA),the crystallization of the perovskite and the photoelectric performance of the corresponding device had been improved,but these improvements were limited at low level.After fluorinated and polymerized DPA,oligomer FO-19 was successfully applied to passivate defects in MAPbI₃.The high-resolution transmission electron microscopy(HRTEM)images showed that FO-19existed at the grain boundaries of the perovskite film and achieved a wrapping effect on the perovskite crystals.Due to the wrapping effect of FO-19,the defects of the perovskite film could be effectively passivated,thereby inhibiting undesirable non-radiative recombination.As a result,FO-19 gifted a PCE of 21.23%for the inverted MAPbI₃-based PSCs,which was among the highest reported values in literatures.In addition,due to the wrapping mode of FO-19,the corresponding device with FO-19 exhibited significantly improved humidity and thermal stability.In this thesis,the key functional layers of inverted PSCs were modified by biomaterials.As a result,an effective low-cost non-fullerene ETL,the effective modification of HTL and the preparation of high-quality perovskite films were achieved,so as to improve the device photovoltaic performance and stability.