Inorganic/organic hybrid solar cells: optimal carrier transport in vertically aligned silicon nanowire arrays

Abstract

Inorganic/organic hybrid radial heterojunction solar cells that combine vertically-aligned n-type silicon nanowires (SiNWs) with poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) have great potential for replacing commercial Si solar cells. The chief advantage of such solar cells is that they exhibit higher absorbance for a given thickness than commercial Si solar cells, due to incident light-trapping within the NW arrays, thus enabling lower-cost solar cell production. We report herein on the effects of NW length, annealing and surface electrode on the device performance of SiNW/PEDOT:PSS hybrid radial heterojunction solar cells. The power conversion efficiency (PCE) of the obtained SiNW/PEDOT:PSS hybrid solar cells can be optimized by tuning the thickness of the surface electrode, and the etching conditions during NW formation and post-annealing. The PCE of 9.3% is obtained by forming efficient transport pathways for photogenerated charge carriers to electrodes. Our approach is a significant contribution to design of high-performance and low-cost inorganic/organic hybrid heterojunction solar cells.

Configuration Effect of Antireflection Layer on Photovoltaic Performance of Silicon/PEDOT:PSS Hybrid Solar Cells

“…For the Si substrate with such micro-textured surfaces, the PEDOT:PSS layer, which is a p-type-like conjugated conducting polymer, was spin-coated at a spin speed of 7500 rpm. We have previously confirmed that for micro-pyramidal structures [11] and nanowire array structures [19] this spin speed enables the PEDOT:PSS layer to better adhere on micro-textured surfaces. The morphology of the PEDOT:PSS layer on the micro-desert textured surfaces and honeycomb surfaces was analyzed by means of cross-sectional SEM micrographs, as shown in Figures 2a and 2b, respectively.…”

“…Thus, the micro-desert textured hybrid solar cell showed a low J sc value owing to the reduced collection rate of the separated electrons at the rear electrode by the occurrence of carrier recombination. In contrast to the J sc value, the high V oc value was related to the high shunt resistance (R sh ), which caused low power losses in the hybrid solar cells [19] , whereas the high FF arose from the low series resistance (R s ). The micro-desert textured hybrid solar cell had a high R sh value of 5.41 × 10 1 Ωcm 2 , and a low R s value of 1.15 Ωcm 2 in comparison with the honeycomb structured cell because of the complete adhesion of the PEDOT:PSS layer throughout the micro-desert textures.…”

“…This implies that most of hole in the PEDOT:PSS layer can be laterally transferred between the Ag fingers with spacing of 500 μm. We have previously attained the high PCE of 9.3% for vertically aligned Si nanowire/PEDOT:PSS hybrid solar cells with such Ag finger-grid front electrode [19] . Thus, although the spacing of 500 μm between the Ag fingers is sufficient for the hole collection at Ag electrode, the reduction in the spacing might be further improved the collection rate of hole.…”

“…The J sc of the micro-desert textured and honeycomb structured hybrid solar cells were raised to more than 30.7 mA/cm 2 after this annealing at 200°C (Figure 4b and Table 1). We have previously reported that the contact resistances between the Ag front electrode and PE-DOT:PSS layer, and between the Al rear electrode and the back side of Si substrate are dramatically reduced by annealing the sample at 200°C for vertically aligned Si nanowire/PEDOT:PSS hybrid solar cells [19] . This is because the annealing process can provide an effective tool for obtaining better adhesion between each electrode and PEDOT:PSS layer/Si substrate [19] .…”

“…We have previously reported that the contact resistances between the Ag front electrode and PE-DOT:PSS layer, and between the Al rear electrode and the back side of Si substrate are dramatically reduced by annealing the sample at 200°C for vertically aligned Si nanowire/PEDOT:PSS hybrid solar cells [19] . This is because the annealing process can provide an effective tool for obtaining better adhesion between each electrode and PEDOT:PSS layer/Si substrate [19] . Moreover, Vosgueritchian and Bao et al, have reported that the annealing process enhances the electrical conductivity of the PEDOT:PSS layer [17] .…”