Inorganic Nanocomposites of n‐ and p‐Type Semiconductors: A New Type of Three‐Dimensional Solar Cell

Abstract

The major drawback of the present generation of photovoltaic solar cells is their laborious, energy-consuming, and costly production. Therefore, a completely new approach is desirable. With the advent of dye-sensitized (Grätzel-type) solar cells, [1] C 60 /polymer, [2] and hybrid CdSe/polymer bulk heterojunctions, [3] a potential alternative is offered, although some serious complications have still to be tackled. A major concern in these alternatives is their poor stability when operating in full sunlight. The cells must be sealed completely against oxygen and water. All-solid, completely inorganic bulk heterojunctions will not require expensive sealing and have been pursued with limited success so far. Here we report a new approach towards what we call the 3D solar-cell concept. We employed atomic-layer chemical vapor deposition (AL-CVD) to infiltrate CuInS 2 inside the pores of nanostructured TiO 2 . In this way it is possible to obtain a nanometerscale interpenetrating network between n-type TiO 2 and p-type CuInS 2 . Since alignment of the conduction bands is required, an In 2 S 3 buffer layer is applied first. Our cells show photovoltaic activity between 360 and 900 nm with a maximum monochromatic incident photon-to-current conversion efficiency of 80 %. When AM 1.5 irradiation is applied the open-circuit voltage is 0.49 V, the short-circuit current is 18 mA cm ±2 , and the fill factor is 0.44, which converts to an overall energy conversion efficiency of 4 %. This is twice the performance of the best inorganic 3D solar cell reported so far.When pursuing the construction of nanometer-scale interpenetrating networks, one faces the question as to how to obtain such a nanocomposite. This question is even more relevant when n-type and p-type semiconductors are to be blended, since in that case, the concentration of impurities and defects must be kept low and the interfaces need to be passivated. Wet-chemical deposition of CuI [4] and CuSCN [5]

Photovoltaic and photoelectrochemical conversion of solar energy

“…Photovoltaic performance data for a 'champion' cell are shown in figure 6. Solid-state equivalents using organic hole-conductors have attained 4.2% efficiency (Schmidt-Mende et al 2005) whereas nanocomposite films comprising only inorganic materials, such a TiO 2 and CuInS 2 have achieved efficiencies between 5 and 6% (Nanu et al 2004(Nanu et al , 2005, significantly more than the recently reported CdTe/CdSe particle-based heterojunctions (Gur et al 2005). Organic PV cells based on blends of a fullerene derivative with poly(3-hexylthiophene) have a confirmed conversion efficiency of 4.8% (Schilinsky et al 2006).…”

“…(i) It renders possible efficient light harvesting by the surface absorbed sensitizer (Nanu et al 2004). On a flat surface a monolayer of dye absorbs at most a few per cent of light because it occupies an area that is several hundred times larger than its optical cross-section.…”

The advent of mesoscopic injection solar cells

“…Solid-state equivalents using organic hole-conductors have exceeded 4% efficiency 5 whereas nanocomposite films comprising only inorganic materials, such as TiO 2 and CuInS 2 have achieved efficiencies between 5 and 6 %. 6,7 New dyes showing increased optical cross-section and capable of absorbing longer wavelengths are currently under development. Similarly, the performance of mesoscopic TiO 2 films employed as electron collectors is benefiting greatly from recent advances in nano-material research.…”

A parametric study of TiO2/CuInS2nanocomposite solar cells: how cell thickness, buffer layer thickness, and TiO2particle size affect performance

“…Among the inorganic nanostructured solar cell concepts, the extremely-thin absorber (ETA) cell [6][7][8][9] has been particularly successful. The 3D nanostructured TiO 2 /CIS solar cell, based on a nanoscale interpenetrating structure between n-type TiO 2 and p-type CuInS 2 (CIS), is a relatively recent inorganic-based design in this field [10].…”