Hybrid Carbon Nanotube/Silicon Schottky Junction Solar Cells

Abstract

In this work, highly transparent and conductive multi-wall-carbon nanotubes (MW-CNTs) are employed to realize solution-processed, hybrid silicon (Si) Schottky -junction solar cells. We first describe the optimization of device structures on silicon wafers with nanowire and micro-pyramidal surface textures, and compare the device characteristics with those of hybrid cells based on Si and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS). The optimized processing conditions include the length of silicon nanowires, the annealing temperature, and the shading ratio of the frontal silver grids. It is found that the hybrid CNT cells outperform the hybrid PEDOT: PSS counterpart under individually optimized processing conditions due to better transparency and conductivity of CNTs than PEDOT: PSS. The best hybrid CNT cells, fabricated using a 14% grid shield ratio, 150 degrees C annealing temperature, and 150nm nanowire length, achieve a PCE of 11.90% and 13.82% in micro-pyramid and nanowire (NW) textured silicon, respectively, in contrast to 7.43% and 12.96% for hybrid PEDOT: PSS cells. To control the rear surface recombination, we further employ two solution-processed, small-molecule materials, Tris(8-hydroxyquinolinato) aluminium (Alq(3)) and 1,3-bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazol- 5-yl) benzene (OXD-7) via a blade-coating technique between the silicon wafer and aluminum electrode. As a result, the PCE of hybrid CNT/Si NW solar cells is enhanced to 13.92% and 14.41% with the insertion of the Alq3 and OXD-7 rear interlayer, respectively. With the high power conversion efficiency (PCE), manufacturing Si-based solar cells at temperatures below 150 degrees C without high vacuum conditions not only significantly lowers the fabrication cost, but also enables the use of ultrathin substrates to save on the material cost for the future.