Hybrid Organic Silicon Solar Cells Using a Carbon-Nanotube Doped PEDOT:PSS Hole Selective Layer
Li-Jung Kuo, ChihLin Chiu, Peichen Yu
National Chiao Tung University, Hsinchu, Taiwan

    A high-efficiency silicon solar cells require superior carrier selective contacts to reduce the minority carrier recombination, which is accomplished by a highly doped n and a p-type layer. In recent years, researchers search for dopant-free carrier-selective material, such as transition metal oxides, alkali metal fluorides, organic materials etc., to replace the complex diffusion or deposition process. Among those, organic materials show great potential due to their capability of the low-temperature solution process. Specifically, hybrid organic silicon solar cells employing the back PEDOT concept have been proposed with over 20% power conversion efficiency. As a results, PEDOT:PSS could be an efficient carrier selective layer. In this work, we employ carbon nanotube (CNT) doped PEDOT:PSS to increase the conductivity and evaluate the potential of CNT-doped PEDOT:PSS as a hole selective layer for conventional silicon solar cell. Two types of PEDOT: PSS noted as TC100, TC200 with a relatively high and low CNT concentrations are investigated through the lifetime measurement, analyses of contact resistivity, the effect of surface passivation and band alignment, as well as the device characteristics. The results have shown that PEDOT: PSS could effectively passivate the silicon surface, especially on the n-type wafer with a minority carrier lifetime of ~240μs. The contact resistivity for holes is also four times smaller than that for electrons on a polished flat surface. Finally, conventional n+/p solar cells with a flat polished or micro-pyramidal textured rear surfaces are incorporated with the TC100 and TC200 PEDOT:PSS hole selective layer. The results have shown that the PEDOT:PSS increase the open-circuit voltage, and short-circuit current, compared to the reference counterpart, by acting as a back-surface field due to its high conductivity. A power conversion efficiency of 14.55% has been achieved for the device with the TC100 hole selective layer.