Richa Pandey
University of Minnesota
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Publication
Featured researches published by Richa Pandey.
Applied Physics Letters | 2012
Richa Pandey; Yunlong Zou; Russell J. Holmes
In this work, we describe the performance of organic photovoltaic cells (OPVs) based on the electron donor-acceptor pairing of boron subphthalocyanine chloride (SubPc) and C70. As an acceptor, C70 is a promising alternative to C60 due to its red-shifted absorption edge and large extinction coefficient, permitting increased photocurrent generation. In uniformly mixed OPVs based on SubPc:C70, peak power conversion efficiency is realized in devices containing 80 wt. % C70. Further enhancement in device performance can be realized through the use of a continuously graded donor-acceptor heterojunction. The optimized graded heterojunction OPV shows a power conversion efficiency of ηP = (5.4 ± 0.2)% under simulated AM1.5 G solar illumination at 100 mW/cm2. This efficiency is significantly larger than the value of ηP = (4.5 ± 0.1)% realized using C60 due to a substantial increase in the short-circuit current density.
Applied Physics Letters | 2012
Richa Pandey; Russell J. Holmes
We demonstrate a technique for determining the charge collection efficiency (ηCC) in bulk heterojunction organic photovoltaic cells (OPVs). To extract ηCC, we describe an approach to measure the optical absorption efficiency by examining the external quantum efficiency under reverse bias. Using estimates of the exciton diffusion efficiency obtained from photoluminescence quenching measurements, ηCC is calculated without any input from optical field simulations. For bulk heterojunction OPVs based on the donor-acceptor pairing of boron subphthalocyanine chloride and C60, a peak ηCC of (79 ± 2)% is realized for films containing 80 wt. % C60 under short-circuit conditions. This optimum composition also coincides with a peak in the fill factor and the short-circuit current density.
Applied Physics Letters | 2012
S. Matthew Menke; Richa Pandey; Russell J. Holmes
Broadband photodetection is achieved by integrating three electron donor materials with complementary absorption into an organic photodetector (OPD). While a single donor-acceptor heterojunction can show broadband response, the spectral tunability is intrinsically limited to the absorption profiles of the active materials. Here, we demonstrate broadband OPDs consisting of multiple bulk heterojunctions arranged in tandem. These OPDs show high responsivity under moderate reverse bias from the ultraviolet to the near-infrared. By combining materials with complementary absorption in a tandem OPD, we demonstrate that the response from each band can be separately tuned with manipulation of the heterojunction thicknesses or composition.
Applied Physics Letters | 2013
Margaret Young; Christopher J. Traverse; Richa Pandey; Miles C. Barr; Richard R. Lunt
Integration of transparent photovoltaics into the building envelope creates unique opportunities to reduce the levelized electricity cost of solar power. However, this integration warrants consideration of the angular dependence of these devices as illumination around the building envelope is rarely at normal incidence. Here we correctly update transfer-matrix and equations to accurately model the quantum efficiency and optical properties under oblique illumination. We use this model to demonstrate the various angular performance characteristics possible for proof-of-concept optimizations of transparent planar-heterojunction solar cells and discuss considerations needed to fully account for optical, electrical, and positional configurations in this optimization.
IEEE Journal of Selected Topics in Quantum Electronics | 2010
Richa Pandey; Russell J. Holmes
We demonstrate enhanced organic photovoltaic cell (OPV) efficiency through the use of continuously graded donor-acceptor (D-A) heterojunctions. Device performance is a strong function of both D-A grading and overall composition ratio. The use of a tunable gradient permits an increase in the D-A interface area for high-exciton diffusion efficiency relative to a planar heterojunction, while also improving the charge collection efficiency relative to a uniform mixture. Using the archetypical D-A pair of copper phthalocyanine and C60, a power conversion efficiency of ηP = (2.1 ± 0.1)% is realized under 100 mW/cm2 simulated AM1.5G solar illumination for a graded heterojunction. This represents an improvement in ηP of ~60% relative to a planar heterojunction OPV and ~20% compared to a uniformly mixed heterojunction OPV.
Advanced Functional Materials | 2012
Richa Pandey; Aloysius A. Gunawan; K. Andre Mkhoyan; Russell J. Holmes
Advanced Materials | 2010
Richa Pandey; Russell J. Holmes
Organic Electronics | 2013
Richa Pandey; Ross Kerner; S. Matthew Menke; James Holst; Kanth V. B. Josyula; Russell J. Holmes
Archive | 2010
Russell J. Holmes; Richa Pandey
Archive | 2013
Russell J. Holmes; Richa Pandey; Stephen Matt Menke