Solar Cells Based on Junctions between Colloidal PbSe Nanocrystals and Thin ZnO Films

Abstract

We report a new type of excitonic solar cell based on planar heterojunctions between PbSe semiconductor nanocrystals and thin ZnO films. These solar cells generate large photocurrents and higher photovoltages compared to Schottky cells assembled with similar nanocrystal films. When illuminated with 100 mW/cm(2) simulated AM1.5 spectrum, these solar cells exhibit short-circuit currents between 12 and 15 mA/cm(2), open-circuit voltages up to 0.45 V, and a power conversion efficiency of 1.6%. The photovoltage depends on the size of the nanocrystals, increasing linearly with their effective band gap energy.

Selective contacts drive charge extraction in quantum dot solids via asymmetry in carrier transfer kinetics

“…The successful operation of CQDs in an efficient solar cell is strongly dependent on the material-processing strategies used in film formation. When CQD are synthesized in solution, they are usually capped by organic molecules that employ long chains (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) carbons) to avoid agglomeration. Optimum photovoltaic operation of the CQD film requires the replacement of such ligands with short organic bidentate linkers, such as ethanedithiol or mercaptopropionic acid (MPA).…”

“…Interfacial engineering to obtain efficient electrical contacts is a central effort of the field 8 . It has been recognized that contacts determine device operation for CQD films used in applications of solar cells as well as photodetectors, which has led to the investigation of different materials such as MoO 3 hole-selective layers, organic and nanostructured contact materials [9][10][11][12][13] .…”

“…To date, drift has been the principal means by which CQD solar cells have extracted their photocurrents 2,3,15,16 . Typical CQD films are doped to an extent N D E10 16 À 10 18 cm À 3 , usually p-type 5,13 , although n-type active layer devices have recently been achieved 17 .…”

Controlled Chemical Doping of Semiconductor Nanocrystals Using Redox Buffers

“…Chemical doping methods reported [6][7][8][9] to date have primarily relied on exergonic reactions in which stoichiometric or kinetic limitations are used to control the degree of doping instead of direct modulation of the Fermi level under equilibrium conditions. For these approaches, the final doping density and homogeneity within the nanocrystal film is a complex convolution of unknown reaction rates for charge transfer, surface coordination, and/or diffusion.…”

“…Figure 4a shows that the source-drain characteristics of a freshly fabricated EDTtreated PbSe nanoparticle transistor exhibits ambipolar behavior, consistent with previous results for thiol-capped lead chalcogenide nanoparticles. 5,8 The source-drain current increases and saturates for both positive and negative values of the gate voltage, indicating injection of both electrons and holes, respectively. The ambipolar nature of the FET is also evidenced by the distinctive takeoff of current in the negative sweep direction as a result of carrier recombination.…”