Fabrication And Study Of Si-PEDOT:PSS Hybrid Solar Cells

Silicon-organic hybrid solar cells have recently attracted great attention because they combine the advantages of silicon (Si) and the organic photovoltaic.Poly(3,4ethylenedioxythiophene)/poly (styrenesulfonate) (PEDOT:PSS), as one of the most hole-conductivity and light-transparent polymer, has been always used to construct Si-PEDOT:PSS hybrid solar cells with N-type Si substrates. Up to now, the power conversion efficiency (PCE) of Si-PEDOT:PSS hybrid solar cells has been boosted as results of efforts in several areas including interface modification, surface texturing on Si, back contact improving, inversion effect strengthening at frond-side and property tuning of PEDOT:PSS, etc..In this study, in order to improve the performance of the Si-PEDOT:PSS hybrid solar cells, several attempts have been done, including insertion of a patterned passivation layer on the back of the Si-substrate to suppress the surface recombination velocity and thus to boost the Voc and PCE, fabrication of novel nanocones structures by simplified metal-assisted chemical etching process for delivering better light trapping effect and more suitable configurations for Si-PEDOT:PSS hybrid solar cells,and the foundation of a simulation model to well predict the light absorption and transmission behaviors of the PEDOT:PSS and antireflection layer. The main achievements are summarized as following:(1) In order to passivate the N-type Si-substrate, we deposited SiNx:H and Al2O3 layers by plasma enhanced chemical vapor deposition (PECVD) and atomic layer deposition (ALD), respectively. During the PECVD process we optimized serval steps including the air flow rate, temperature of substrate, deposition power, thickness of the film , etc. Ultimately, we obtained the passivation level for SiN,:H films with a surface recombination rate of about 30 cm/s. Similar optimization steps have been done to improve the passivation level of Al2O3 film, including adjusting thickness, improving annealing conditions, etc. In the end, a Al2O3 film with a surface recombination rate of about 30 cm/s was achieved. After technological conditions exploration, both SiNX:H and Al2O3 films show great passivation capabilities to Si wafers, and the results obtained in this part also provided the solid supporting for the following research about rear-sided passivation by dielectric layer for improved Si-PEDOT:PSS hybrid heterojunction solar cells.(2) We apply SiNx:H and Al2O3 films to passivate the back side of Si substrate.Patterned SiNx:H and Al2O3 passivation films were formed on the rear-side of Si substrates by using photolithography and HF etching process. By comparing the surface minority carrier lifetime, the SiNx:H layer with better passivation effect was applied to the Si-PEDOT:PSS hybrid solar cell enabling an improvement of 0.6 % in the PCE. The addition of the SiNx:H layer boosted the open circuit voltage (Voc) from 0.523 to 0.557 V, suggesting the well-passivation property of the patterned SiNx:H thin layer that was created by plasma-enhanced chemical vapor deposition and lithography processes. The passivation properties that stemmed from front PEDOT:PSS, rear-SiNx:H, front PEDOT:PSS/rear-SiNx:H, etc. are thoroughly investigated, in consideration of the process-related variations.(3) We developed a simplified metal-assisted chemical etching method to deliver front-side surface texturing with hierarchically nanocones on Si-substrate. The improved method enable to initiate the synchronous reactions of Ag particles deposition and black-Si etching process in only one solution. In order to fabrication hierarchically nanocones, we carried out the ecthing process two times. After optimizing the soaking time, we fabricated hierarchically nanocones with an omnidirectional light harvesting over the entire solar spectrum. The nanocones-based Si-PEDOT:PSS cells achive a PCE up to 11.75 %., which is much larger than the reference devices of 9.91 % under an air mass 1.5 G irradiation. This improvement is attributed to the enhanced contact area that comes from the hierarchically nanocones configurations.(4) Molybdenum oxide (MoO3) is one of most suitable antireflection (AR) layers for Si-PEDOT:PSS hybrid solar cells due to its well-matched refractive index (2.1). A simulation model was employed to predict the optical characteristics of Si-PEDOT:PSS hybrid solar cells with the MoO3 layers as antireflection coatings (ARCs), as well as to analyze the loss in current density. By adding an optimum thickness of a 34-nm-thick ARC of MoO3 on the front side and an effective rear back surface field (BSF) of phosphorus-diffused N+ layer at the rear side, the hybrid cells displayed higher light response in the visible and near infrared regions, boosting a short-circuit current density(Jsc) up to 28.7 mA/cm2. The average PCE of the Si-PEDOT:PSS hybrid solar cells is 11.90 %, greater than the value of 9.23 % for the reference devices.