Charge transport in hybrid nanorod-polymer composite photovoltaic cells

Abstract

Charge transport in composites of inorganic nanorods and a conjugated polymer is investigated using a photovoltaic device structure. We show that t he current-voltage (I-V) curves in the dark can be modelled using the Shockley equation modified to include series and shunt resistance at low current levels, and using an improved model that incorporates both the Shockley equation and the presence of a space charge limited region at high currents. Under illumination the efficiency of photocurrent generation is found to be dependent on applied bias.Furthermore, the photocurrent-light intensity dependence was found to be sublinear. An analysis of the shunt resistance as a function of light intensity suggests that the photocurrent as well as the fill factor is diminished as a result of increased photoconductivity of the active layer at high light intensity. By studying the intensity dependence of the open circuit voltage for nanocrystals with different diameters and thus band gaps, it was inferred that Fermi-level pinning occurs at the interface between the aluminum electrode and the nanocrystal.3

Progress on a Photovoltaic Cell Design Consisting of Silicon Nanowires and Poly (3‐ hexylthiophene)

“…The energy difference between the HOMO and LUMO states may be regarded as the band gap ganic semiconductor, yet a thin polymer film cannot be fully described by the band model [31,40]. While, like an inorganic semiconductors, the energy gap between the HOMO and LUMO states is equal to the E OG , it is not equal to the E EG between charge carriers.…”

“…S s do not merge completely to form a continuous energy band, the exciton that is formed upon the absorption of a photon into an organic semiconductor lattice is confined to the localized LUMO state of the absorbing molecule (see Figure 6b). The electrically neutral [31,48] exciton propagates through the semiconductor by hopping from one LUMO state to the next via thermal energy transfer [17]. This diffusion, therefore, is random and may be in any direction [38].…”

“…band off-set energies and kinetic factors [31,41]), the rate of charge recombination are many orders of magnitude slower than the rate of charge separation [38,42].…”

“…SiNWs could potentially be considerably cheaper to produce than either c-Si or a-Si while retaining the capacity for high degrees of crystallinity and purity. P3HT has been shown to absorb more of the optical spectrum than other polymer semiconductors [2,19,[28][29][30]32,33] and has the highest reported mobility [15,29,31]. P3HT also offers the advantage of a variety of wet processing methods which are easily upgradeable to large scale production [19].…”

“…Due to the improved stacking of the molecules [18,31,32], regioregular P3HT would be preferable [56,57] with reported mobilities between ~10 -4 to 0.1 cm 2 V -1 s -1 [29,58]. The degree of crystallininty in P3HT thin films may be controlled with the processing conditions (e.g.…”