Optimization Of The Hole Transport Layer Of Perovskite Solar Cell

Organic inorganic halide perovskite, possessing the desirable properties of high absorption coefficient, very low material costs, long charge diffusion length, appropriate bad gap, and solution processability, shows great potential for photovoltaic applications. Within just five years, the power conversion efficiency(PCE) of the perovskite solar cell(PSC) has risen from 3.8% to 20%. The issues of the degradation of perovskite should be urgently addressed to achieve good reproducibility and long lifetimes for PSC. Without studies on stability, exciting achievements cannot be transferred from the laboratory to industry and outdoor applications. In this thesis, we aim to improve the power conversion efficiency and stability of the PSC by optimizing the hole transport layer.1. Designing MoO3/PEDOT:PSS hole transport bilayer in PSC. MoO3 is inserted between ITO conductive glass and PEDOT:PSS layer to prepare hole transport bilayers, the optimized device structure is ITO/MoO3/PEDOT:PSS(40 nm)/CH3NH3PbI3(350 nm)/C60(40 nm)/Bphen(5 nm)/Ag(100 nm). The incorporation of an MoO3 layer does not affect the growth of PEDOT:PSS, but dramatically improves the PCE and stability of the device. The as-prepared optimized device shows a PCE of 12.78%, which is increased by about 30% as compared with the reference device based on pristine PEDOT:PSS. The improvement is attributed to the increased hole collection efficiency with an MoO3 layer. A maximum PCE of 14.87% is obtained for the device after a short storage under ambient conditions in the dark, which is one of the highest PCE reported for inverted planar heterojunction(PHJ) PSC. More importantly, only 7% degradation in PCE is observed for the optimal device and almost complete failure of the reference device for storage under ambient conditions for 10 days. This work has provided a simple strategy to simultaneously improve the PCE and stability of PHJ PSC.2. High efficiency and stable hole transporting material-free(HTM-free) PHJ PSC is constructed by directly thermal evaporating perovskite materials onto indium tin oxide substrate. The optimized device structure is ITO/CH3NH3PbI3-xClx(35 nm)/C60(40 nm)/Bphen(5 nm)/Al(100 nm). A condense and homogeneous morphology is found for this perovskite film even without any annealing process. The optimized HTM-free CH3NH3PbI3-xClx/C60 PHJ device with a 35 nm ultra-thin CH3NH3PbI3-xClx layer presents a high hole extraction efficiency and a low charge carrier recombination probability, which results in a high short circuit current and fill factor. The HTM-free device shows a high power conversion efficiency of 8.37%, which is one of the highest efficiency among reported inverted HTM-free PSCs even that a thinner perovskite film is used. More importantly, the device also exhibits a superior stability in ambient condition. The related experiment provides a simple and efficient perovskite structure.3. Design and apply CuI/PbPc as HTL in PSC. The CuI/PbPc layer is prepared by vacuum deposition method and the perovskite thin film by solution spin coated. The optimized device structure is ITO/CuI(2 nm)/PbPc(20 nm) /CH3NH3PbI3(350 nm)/C60(40 nm)/Bphen(5 nm)/Ag(100 nm). We found that the Cu I/PbPc as HTL perform a comparable efficiency to PEDOT:PSS, and largely enhance the stability of PSC in high humidity. The as-prepared optimized device reach the maximum PCE of 9.61% after storage in ambient conditions in dark for 6 days. More importantly, the optimized device retains 73% of its best PCE when they were stored in ambient conditions for 21 days, compared to an almost full failure for the reference device after 6 days, and interestingly, Voc remains unchangeable even in nearly two months test. Experiments show that the CuI/PbPc HTL can significantly improve device stability in the surrounding atmosphere.