[BNC-all] Prelim exam (Feb-7): Performance limits of solar cells

[Mohammad Ryyan Khan]

Hello,

Just a reminder about my prelim talk today (please see details below).

Regards,
M. Ryyan Khan

On 2/3/2014 11:21 AM, Mohammad Ryyan Khan wrote:
> Hello,
>
>  I would like to invite you all to my prelim talk.
>
> Date:         Feb.7.2014
> Time:         3:30pm
> Location:   BRK 1001
>
>
> Title: *Performance limits of solar cells*
>
> /Abstract:/
>
> The solar cell device concepts can be broadly classified into two
> groups: (i) high efficiency crystalline cells with efficiencies
> approaching the thermodynamic limit, and (ii) lower cost thin film
> alternatives that offer improved cost-efficiency tradeoffs.  For the
> first group, the challenge is to develop a meticulous understanding of
> cell operation so that the remaining efficiency gap can be closed. For
> the second group, the challenge is to develop a material-specific
> understanding of cell operation to improve the efficiency and
> reliability of the cell.
>
> /_First_/, in an effort to explore the limits of cell operation for
> both types of technologies, we have studied the thermodynamics limit
> of PV operation from a new perspective of a 2-level solar cell. Our
> approach provides qualitative and intuitive understanding of the loss
> components in an ideal PV device. The analysis framework also shows
> how the existence of heterojunction (HJ) in organic photovoltaics
> (OPVs) limits the upper bound of performance even for perfect
> absorption and 100% carrier extraction. /_Second_/, we considered the
> detailed balance limit in presence of non-ideal optical response
> (incomplete absorption and existence of non-radiative recombination)
> for a given PV material. This study demonstrates that the
> thermodynamic efficiency limit can be asymptotically reached with
> imperfect absorption---however, designs towards ultra-high efficiency
> systems need to consider non-radiative recombination effect. /_Third
> and finally_/, we considered two major topics of practical systems:
> (i) addressing poor carrier collection (for OPVs), and (ii) general
> light absorption schemes. We have proposed design perspectives and new
> structures to address poor carrier transport in OPVs. These ideas
> involve providing shorter route for carrier to contact paths. Our
> nanowire (NW) based photon absorption scheme has separate tuning
> handles for reflection and absorption---unlike previous NW schemes
> where there was a trade-off between  reflection and absorption. In our
> latest work, we have proposed a light management scheme that can
> perfectly trap the photons that are coupled into the structure. This
> approach has the potential to break the geometric light trapping
> limit, and also can be easily integrated into a planar thin film PV
> device.
>
>
>
> Regards,
> M. Ryyan Khan,
> PhD RA, Prof M. A. Alam,
> ECE, Purdue University
> http://web.ics.purdue.edu/~khan23/
>

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