Abstract
We systematically analyzed the detailed-balance-limit-conversion efficiency of solar cells with quantum dots (QDs) embedded in host materials. We calculated their open-circuit voltage, short-circuit current, and conversion efficiency within single-photon absorption conditions, both in the radiative limit and in other cases with non-radiative recombination loss, using modeled absorption band with various absorptivities and energy widths formed below that of the host material. Our results quantitatively revealed the existence of intrinsic and significant drops in the open-circuit voltage and conversion efficiency of QD solar cells, in addition to extrinsic drops due to degraded material quality.
Highlights
We calculated the detailed-balance-limit value of conversion efficiency as a function of a1 between 0 and 1, which is as explained in the method section[28,29]
We have presented an analysis of the detailed-balance-limit conversion efficiency, short-circuit current, open-circuit voltage, and emission energy of quantum dots (QDs) solar cells with various parameters for the QD-absorption band below the host-material band gap
When the QD-absorption band has absorptivity, a1, of almost 0 or small QD-binding energy Eb below 0.1 eV, the cell is almost identical to a bulk-host-material solar cell
Summary
On the basis of solar cells incorporating quantum structures as wells (QWs) and dots (QDs), vast varieties of new concepts have been studied for improving conversion efficiency, such as increase in short-circuit current (Jsc) via excitonic absorption, multi-exciton generation, and multi-photon-absorption, and as increase in open-circuit voltage (Voc) via reducing mismatch between absorption and emission solid angles[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]. This type of QD solar cells and their experimental data have mostly been compared with IB-solar-cell model theories[1,2]. Experimentally measured Voc and conversion efficiency of QD solar cells have been significantly lowered from bulk host-material solar cells in many cases[4,5,6,7,8,9] The mechanism for these phenomena has to be investigated quantitatively or systematically. The objective of this work is to use the extended detailed-balance-limit theory to quantitatively analyze the voltage drop and reduced conversion efficiency caused by intrinsic physics in QD solar cells, as apart from the contributions of extrinsically low material quality. The same argument could be generally possible including the cases for QD and other quantum-structured solar cells, but no systematic or detailed study has been reported on this point
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