AVS 56th International Symposium & Exhibition
    Electronic Materials and Processing Tuesday Sessions
       Session EM1+PV-TuM

Paper EM1+PV-TuM4
PbSe Quantum-Dot Solar Cells

Tuesday, November 10, 2009, 9:00 am, Room A8

Session: High Efficiency and Quantum Structure Photovoltaics
Presenter: E.S. Aydil, University of Minnesota
Authors: K.S. Leschkies, University of Minnesota
T.J. Beatty, University of Minnesota
M.S. Kang, University of MInnesota
D.J. Norris, University of MInnesota
E.S. Aydil, University of Minnesota
Correspondent: Click to Email
Quantum confinement of electrons and holes in nanometer size crystals (quantum dots or QDs), endows them with properties that may be advantageous for efficient solar-to-electric energy conversion. First, electronic energy levels and optical absorption in QDs can be manipulated by changing their size. This allows the optimization of their optical absorption for maximum overlap with the solar spectrum. Second, the ability to manipulate energy levels through size raises the possibility to make inexpensive multijunction solar cells by judiciously layering different size QDs. Third, it has been suggested that quantum confinement may slow energy dissipative electron and hole relaxation rates such that two new physical processes, multiple exciton generation and hot electron extraction may now compete with relaxation and lead to higher photocurrents or higher photovoltages, respectively. Finally, QDs can be prepared in large quantities as stable colloidal solutions under mild conditions and deposited on surfaces of various planar or nanostructured substrates as thin films through inexpensive high-throughput coating processes to form photovoltaic devices. For these reasons, solar cells based on QDs may have the potential to achieve high power conversion efficiencies at low cost and are promising candidates for third generation photovoltaic devices. We report a new type of solar cell based on heterojunctions between PbSe QDs and thin ZnO films. We find that the photovoltage depends on the QD size and increases linearly with the QD effective band gap energy. Thus, our solar cells resemble traditional photovoltaic devices based on a semiconductor-semiconductor heterojunction but with the important difference that changing the size of the QDs can vary the band gap of one of the semiconductors and hence the cell’s photovoltage. Under simulated 100 mW/cm2 AM1.5 illumination, these QD solar cells exhibit short-circuit currents as high as 15 mA/cm2 and open-circuit voltages up to 0.45 V. Overall power conversion efficiency of the best device to date is 1.6% but may be increased further using nanostructured interfaces between PbSe QDs and ZnO. Moreover, we show evidence that this new solar cell may be operating like an excitonic solar cell rather than a traditional p-n junction solar cell.