The Role of Hole Transport in Hybrid Inorganic/Organic Silicon/ Poly(3,4-ethyienedioxy-thiophene):Poly(styrenesulfonate) Heterojunction Solar Cells

摘要

In this paper, the fundamental advantage of highly conductive transparent polymers as hole transport layers in hybrid solar cells is demonstrated. The substantial efficiency improvement of hybrid n-type silicon (n-Si)/poly(3,4-ethylenedioxy-thiophene):poly-(styrenesulfonate) (PEDOT:PSS) solar cells by adding organic solvents to the polymer dispersion is investigated, and a model that explains reasons and mechanisms for that improvement is given. Open-circuit voltages of 600 mV were measured, which are comparable to conventional diffused silicon pn-junction wafer cells. It is shown by means of X-ray photoelectron spectroscopy that the PEDOT versus PSS ratio plays an important role for charge carrier transport in the PEDOT:PSS layer as well as for charge carrier separation at the n-Si/PEDOT:PSS interface. A shell of insulating PSS segregates at the surface of PEDOT:PSS grains and represents a considerable barrier for charge carrier transport and charge carrier separation, influencing the conductivity of the polymer film and the open-circuit voltage of a processed solar cell, respectively. It could be demonstrated that a mixing of the PEDOT:PSS polymer blend with the organic solvent dimethylsulfoxide reduces the PSS insulator segregation at the surface of PEDOT:PSS grains and improves the performance of hybrid n-Si/PEDOT:PSS solar cells.