Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

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Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

We report for the first time on a hole conductor-free mesoscopic methylammonium lead iodide (CH3NH3PbI3) perovskite/TiO2 heterojunction solar cell, produced by deposition of perovskite nanoparticles from a solution of CH3NH3I and PbI2 in γ-butyrolactone on a 400 nm thick film of TiO2 (anatase) nanosheets exposing (001) facets. A gold film was evaporated on top of the CH3NH3PbI3 as a back contact. Importantly, the CH3NH3PbI3 nanoparticles assume here simultaneously the roles of both light harvester and hole conductor, rendering superfluous the use of an additional hole transporting material. The simple mesoscopic CH3NH3PbI3/TiO2 heterojunction solar cell shows impressive photovoltaic performance, with short-circuit photocurrent Jsc= 16.1 mA/cm2, open-circuit photovoltage Voc = 0.631 V, and a fill factor FF = 0.57, corresponding to a light to electric power conversion efficiency (PCE) of 5.5% under standard AM 1.5 solar light of 1000 W/m2 intensity. At a lower light intensity of 100W/m2, a PCE of 7.3% was m...

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Mesoscopic CH3NH3PbI3/TiO2 heterojunction solar cells.

We describe here a simple, all-inorganic metal/NC/metal sandwich photovoltaic (PV) cell that produces an exceptionally large short-circuit photocurrent (>21 mA cm -2 ) by way of a Schottky junction at the negative electrode. The PV cell consists of a PbSe NC film, deposited via layer-by-layer (LbL) dip coating that yields an EQE of 55-65% in the visible and up to 25% in the infrared region of the solar spectrum, with a spectrally corrected AM1.5G power conversion efficiency of 2.1%. This NC device produces one of the largest short-circuit currents of any nanostructured solar cell, without the need for sintering, superlattice order or separate phases for electron and hole transport.

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Schottky Solar Cells Based on Colloidal Nanocrystal Films

This work is a brief account of the most recent developments observed in the application of ZnO nanostructured materials in excitonic solar cells (organic, hybrid and dye sensitized solar cells). Special emphasis is made to one-dimensional (1D), vertically-aligned nanostructures (nanowires NW, nanorods NR) of ZnO semiconductor oxide and the extensive research work invested in recent years for its application as an electron acceptor material in solar cells. Our aim is to give the reader a broad overview of this semiconductor oxide and to understand the causes, advantages and disadvantages, for its application in a well-aligned nanostructure form. We briefly describe the most applied methodologies for its synthesis as well as the effect on surface area, electron transport and charge recombination when it is applied as an electron transport material in excitonic solar cells (XSCs). The importance of low-cost and easy-scalable synthesis techniques, as well as stability issues on these solar cells are discussed. Finally, we include a brief analysis of the possible future trends for the application of this interesting semiconductor oxide in XSCs.

Vertically-aligned nanostructures of ZnO for excitonic solar cells: a review

Half of the sun’s power lies in the infrared. As a result, the optimal bandgaps for solar cells in both the single-junction and even the tandem architectures lie beyond 850 nm. However, progress in low-cost, large-area, physically flexible solar cells has instead been made in organic and polymer materials possessing absorption onsets in the visible. Recent advances have been achieved in solution-cast infrared photovoltaics through the use of colloidal quantum dots. Here we report stable solution-processed photovoltaic devices having 3.6% power conversion efficiency in the infrared. The use of a strongly bound bidentate linker, benzenedithiol, ensures device stability over weeks. The devices reach external quantum efficiencies of 46% in the infrared and 70% across the visible. We investigate in detail the physical mechanisms underlying the operation of this class of device. In contrast with drift-dominated behavior in recent reports of PbS quantum dot photovoltaics, we find that diffusion of electrons and ...

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Efficient, stable infrared photovoltaics based on solution-cast colloidal quantum dots.

We report a comparison of photoconductive performance of PbS nanocrystal/polymer composite devices containing either oleic acid-capped or octylamine capped nanocrystals (NCs). The octylamine-capped NCs allow over two orders of magnitude more photocurrent under −1V bias; they also show an infrared photovoltaic response, while devices using oleic acid-capped NCs do not. Further improvement in the photovoltaic performance of films made with octylamine-capped NCs occurs upon thermally annealing the composite layer at 220 °C for 1 h. The procedure leads to a 200-fold increase in short circuit current, a 600-fold increase in maximum power output, and an order of magnitude faster response time.

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Enhanced infrared photovoltaic efficiency in PbS nanocrystal/semiconducting polymer composites: 600-fold increase in maximum power output via control of the ligand barrier

S. Zhang

Papers

Enhanced infrared photovoltaic efficiency in PbS nanocrystal/semiconducting polymer composites: 600-fold increase in maximum power output via control of the ligand barrier