![]() ![]() Superiority of SML-QD based solar cell over both the SK-QD and the InGaAs QW based solar cell (SC), is found. Moreover, different coverages of SML InAs have been tested for optimum solar cell performance and near 0.25 ML InAs deposition was found best for solar cell application. This paper reports on an investigation of the comparative performance of different In(Ga)As quantum structure solar cells: (1) SK-QD, (2) SML QD (3) quantum well (QW) and (4) a quasi-ML InAs stack solar cell. Looking at these contrasting reports, it is warranted to reexamine the potential of InAs SML QD for solar cell applications. which suggest the degradation in solar cell efficiency after SML QD and SK QD introduction in pin solar cell. However, there is other report by Lam et al. have shown improved solar efficiency over reference pin junction based solar cell by utilizing SML QD in a paper which compares between SML QD, SK QD, quasi monolayer (QML) QD and reference pin solar cell. Several advantages of SML-QDs over SK-QDs are smaller size, higher dot density and uniformity. SML-QDs are grown by depositing alternate layers of SML InAs (preferably 0.25–0.5 ML) and thin Ga(In)As barriers. Submonolayer QDs, achieve a much smaller QD size, , ] and higher uniformity in size. To explore this trade-off we investigated submonolayer (SML) based InAs QD as an alternative method to the more conventional SK QD. However, this is a trade-off since smaller QDs decreases absorption bandwidth. Trapping mainly depends on the QD size, where smaller QDs will result in reduced trapping. The main reasons for deteriorated efficiency of InAs SK QD based IBSC, are recapturing or trapping of excess carriers and strain-induced defects. ![]() ![]() However, if the V OC degradation could be minimized, then the QD IBSC efficiency can be increased. Consequently, very few reports have shown even a slight enhancement in efficiency over the reference pin solar cell. Devices utilizing this strategy, unfortunately have suffered from degradation in open circuit voltage (V OC), which has ultimately resulted in efficiency degradation in the SK QD based IBSC. By extending the solar absorption spectra, the short-circuit current (I SC) is therefore enhanced. These carriers can then be extracted into the barrier's bands by either a second photon absorption, thermal escape or tunneling. As a result, sub-bandgap photons absorbed in these solar cells promote carriers into the confined states. One experimental realization of an IBSC utilizes vertical stacks of InAs Stranski-Krastanov (SK) QDs embedded in the intrinsic region of a GaAs pin diode for the sub-bandgap electronic states. However, when adding an intermediate band to a SC, there is agreement that a quasi-fermi level discontinuity (ΔQFL) is needed between the intermediate band and the conduction band (CB), to maintain the open circuit voltage (V OC) of the SC. Efficiency enhancement by IBSC has been the topic of intense investigation and debate since its inception, ,, ,, , ]. For example, the enhancement in efficiency can be accomplished by extending the solar absorption spectra of a semiconductor by capturing sub-bandgap photons via a narrow band of electronic states that exist within the semiconductor energy band gap. ![]() The intermediate band solar cell (IBSC) concept was proposed to enhance the solar cell (SC) efficiency over the Schockley-Queisser thermodynamic limit of a single junction solar cell. ![]()
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