Photoelectric Properties Of High Efficiency Crystalline Silicon-Organic Heterojunction Solar Cells

Combining heterojunctions structure with interdigitated back contacts,crystalline silicon(c-Si)solar cells have recently achieved record photoelectric conversion efficiencies(PCEs)of 26.6%.However,due to the inherent parasitic absorption/Auger recombination of the highly doped amorphous Si layers,and the complex fabrication process requirements of the p~+and n~+heterojunction contact,such solar cells still exist serious photoelectric loss and technical constraints.These problems have prompted people to seek alternative new functional materials and simplified deposition techniques.Dopant-free carrier-selective c-Si/organic heterojunction solar cells(HSCs)withn-typec-Siasabsorberandpoly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(n-Si/PEDOT:PSS)as hole-selective conducting layer,emerge as promising solution-processed,low-cost photovoltaic devices.However,at the present stage,their PCEs are still much lower than c-Si solar cells.In this thesis,we focus on the designing and fabricating of high-efficiency n-Si/PEDOT:PSS HSCs,and discuss the effects of n-Si/PEDOT:PSS heterojunction interface and pre/post-treatment on the photoelectric properties of HSCs.The main research contents and results are as follows:1.Improving the photoelectric properties of n-Si/PEDOT:PSS HSCs via Si surface chemical pre-treatment.By pretreatment of Si substrate in tetramethylammonium hydroxide solution,the Si surface defect and interfacial oxide layer thickness were well controlled,which resulted in suppressed interfacial carrier recombination.Meanwhile,high work-function copper iodide film was deposited on the surface of PEDOT:PSS film to induce the work-function of PEDOT:PSS film and enhance the heterojunction interface inversion effect.Combining these two treatments,the open circuit voltage and fill factor of the HSCs can be increased to 0.660 V and 78.1%without the use of back surface passivation.The final PCE can be increased to 14.3%.2.Improving the contact performance of n-Si/PEDOT:PSS heterojunction interface by controlling the Si surface nanostructure.Metal-assisted chemical etching process was used to deliver front-side surface texturing of hierarchically bowl-like nanostructure/hexagonally ordered nanocone-nanopillar dual-structured arrays on 20?m c-Si substrate,enabling effective light harvesting over the entire solar spectrum as well as an enlarged contact area with the polymer.Through these improvements,PCE up to 13.6%/12.2%were achieved for n-Si/PEDOT:PSS HSCs.3.Enhanced photoelectric properties of n-Si/PEDOT:PSS HSCs via Si/Al interfacial modification.Dopant-free,carrier-selective n-Si/PEDOT:PSS HSCs were constructed by introducing a narrow bandgap conjugated polyelectrolyte(PTB7-NBr)at the n-Si/Al interface.The n-Si/Al contact resistance can be reduced to 6.7±0.8 m?cm~2 due to the excellent electron transport properties of the brominated ion doped PTB7-NBr layer and its work-function reduction to the Al electrode.Combined with the front-side nanostructure texturing,HSCs with PCE over 15.0%was finally obtained.4.Design and preparation of full-contact n-Si/PEDOT:PSS HSCs.Through post-treatment of the random pyramid-textured n-Si/PEDOT:PSS surface,fully contacted PEDOT:PSS film on textured silicon surface was achieved.In combination with the excellent passivation and electron transport properties provided by the back-intrinsic/doped amorphous silicon layer,PCE exceeding 16.2%was finally achieved.In addition,this post-treatment can effectively protect the PEDOT:PSS film and the underneath interface oxide from moisture,which results in dramatic improvement in stability.This study provides an effective way to improve the stability and efficiency of silicon-organic heterojunction solar cells.