Figure 5: Photocurrent power dependence under anti-Stokes illumination. | Nature Communications

Figure 5: Photocurrent power dependence under anti-Stokes illumination.

From: A hot-electron thermophotonic solar cell demonstrated by thermal up-conversion of sub-bandgap photons

Figure 5

(a) The power dependence of sample A, in which Jpv is comprised of three components: radiative coupling Jrad, direct generation Jdir and emission enhancement due to entering the thermophotonic regime JΔT. The inset diagrams show the sample structure and experimental conditions for the measurements. Sample A is a solar cell with an MQW-based solar collector and sample B is an identical reference solar cell without a solar collector. The lines are linear fits to experimental data showing that the solar cell photocurrent is mainly due to radiative coupling between the solar collector and the solar cell. The data also show that the direct generation component is negligible being four orders of magnitude smaller than other terms. (b) The extracted carrier temperature from anti-Stokes PL shows the onset of carrier heating at 95±30 kW cm−2. The horizontal error bars represent the measurement error in laser intensity and spot size, the vertical errors bars correspond to the standard error associated with the least squares fitting. (c) Fitted power-dependent photocurrent of sample A (black) with linear Jrad (blue) and nonlinear JΔT (red) components. Note that Jdir has been ignored because it contributes negligibly to the overall photocurrent. The data show an onset of carrier heating of 117±25 kW cm−2, which is in good agreement with the value extracted from PL. Horizontal error bars have the same meaning as in b and vertical error bars are the standard error in the photocurrent measurement. (d) Experimentally determined up-conversion efficiency EQEup, which is the ratio of photons per second up-converted to nlaser, the number of entering photons per second from the laser. The thermophotonic regime is indicated in which the optical energy transferred to the solar cell is enhanced due to the solar collector having both a chemical potential and a thermal gradient. The errors bars are calculated by propagating the standard error values from photocurrent data shown in c.

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