Abstract
Hybrid organic-inorganic heterojunction solar cells based on silicon nanowires (SiNWs) are promising candidates for next-generation photovoltaics owing to potentials for low fabrication cost and high efficiency. The SiNW array, fabricated by a simple metal-assisted wet chemical etching method, produces a large surface-area-to-volume ratio, hence allowing efficient light harvesting and charge collection via the formation of a core-sheath p-n junction. However, previously reported power conversion efficiencies (PCEs) are approximately capped at 10~11%, which is largely depicted by the interface defect densities that limit the open-circuit voltage (Voc) and fill factor (FF). In this work, we introduce a solution-processed, intermediate 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) layer to mitigate the interface recombination loss for hybrid heterojunction solar cells consisted of SiNWs and polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The power conversion efficiency reaches a record 13%, which is largely ascribed to the modified organic surface morphology and suppressed saturation current that boost the open-circuit voltage and fill factor. The insertion of TAPC clearly increases the minority carrier lifetime due to large electron barrier presented at the interface. Furthermore, X-ray photoemission spectroscopy confirms that TAPC can effectively block the strong oxidation reaction occurred at the PEDOT:PSS-silicon interface, which improves the device characteristics and promises improvement for reliability. The learning presented in this work point detailed directions for interface engineering towards the attainment of highly efficient hybrid photovoltaics.