An angle resolved X-ray photoemission study of carbon nanotube/ silicon hybrid photovoltaic (PV) cells is reported, providing a direct probe of a chemically inhomogeneous, Si−O buried interface between the carbon nanotube (CNT) networked layer and the n-type Si substrate. By changing the photoelectron takeoff angle of the analyzer, a nondestructive in-depth profiling of a CNT/SiO x / SiO 2 /Si complex interface is achieved. Data are interpreted on the basis of an extensive modeling of the photoemission process from layered structures, which fully accounts for the depth distribution function of the photoemitted electrons. As X-ray photoemission spectroscopy provides direct access to the buried interface, the aging and the effects of chemical etching on the buried interface have been highlighted. This allowed us to show how the thickness and the composition of the buried interface can be related to the efficiency of the PV cell. The results clearly indicate that while SiO 2 is related to an increase of the efficiency, acting as a buffer layer, SiO x is detrimental to cell performances, though it can be selectively removed by etching in HF vapors.

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Processing temperature is highlighted as a convenient means of controlling the optical and charge transport properties of solution processed electron transport layers (ETLs) in inverted polymer solar cells. Using the well-studied active layer -poly(3-hexylthiophene-2,5-diyl) (P3HT):indene-C 60 bisadduct (ICBA) -we show the influence of ETL processing temperatures from 25 °C -450 °C, reporting the role of crystallinity, structure, charge transport and Fermi level (E F ) on numerous device performance characteristics. We determine that an exceptionally low temperature processed ETL (110 °C) increases that device power conversion efficiency (PCE) by a factor greater than 50% compared with a high temperature (450 °C) processed ETL. Modulations in device series and shunt resistance, induced by changes in the ETL transport properties are observed in parallel to significant changes in device open circuit voltage attributed to changes on the E F of the ETLs. Our work highlights the importance of interlayer control in multilayer photovoltaic devices and presents a convenient material compatible with future flexible and roll-to-roll processes.

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