Efficiency of negative-illumination photovoltaic energy conversion

TL;DR

This work investigates negative-illumination photovoltaic (NIPV) energy conversion by mounting infrared p-n junction diodes against a sufficiently cold surface to harvest terrestrial infrared radiation. Using two diodes with different bandgaps, the authors measure external quantum efficiency $b7_Q(T_H)$ and energy conversion efficiency $b7_E(T_H)$, and develop a model where the observed photovoltage is linked to a photocurrent $I_{SC}$ and an internal resistance $R_D$, yielding $b7_E=rac{e b7^2 y(x_g)^2 T_H^2 r_D S}{1+e b7^2 y(x_g)^2 T_H^2 r_D S}$ with $y(x_g)= abla\!\int_{x_g}^{\infty} \frac{x^2}{e^x-1}dx$ and $x_g=E_g/(k_B T_H)$. The experiments observe $b7_Q$ of 10–60% (Diode A higher) while $b7_E$ remains below $10^{-4}\%$, and report a maximum power density around $206\ \mu\mathrm{W/m^2}$ for Diode A at $T_H\approx288\ \mathrm{K}$. Theoretically, increasing the resistance-area product $r_D S$ and optimizing the bandgap (e.g., $E_g\approx0.065\ \mathrm{eV}$ for $T_H=300\ \mathrm{K}$) could substantially raise $b7_E$, though practical limits such as breakdown voltages and quasi-Fermi level considerations bound the achievable efficiency. Overall, the study provides a quantitative framework linking device parameters to performance in thermoradiative energy conversion and points to concrete material strategies to improve heat-to-electricity conversion in narrow-gap semiconductors.

Abstract

Infrared diodes generate electricity from thermal radiation emitted from themselves. The negative process of photovoltaic effect has been expected for application to energy harvesting systems converting from terrestrial radiation. However, its energy conversion efficiency has been known to be very low. In this paper, we investigate energy conversion efficiency and external quantum efficiency for the negative-illumination photovoltaic effect with a systematic measurement for infrared diodes faced to a sufficiently cold surface. We find that the external quantum efficiency reaches 60\ \% for a diode at a temperature, while the energy conversion efficiency stays below 10^-4 %. We indicate dominant parameters for the efficiencies and propose how to improve energy conversion efficiency.

Figures (4)

• Figure 1: (a) Negative-illumination photovoltaic generator as a heat engine. (b) Photovoltage for an InAsSb photovoltaic cell (Diode A) under negative-illumination as a fuction of cold bath temperature. The thin dashed curves are theoretical curves.
• Figure 2: (a) Schematics of experimental setup. (b) Equivalent circuit of a diode device configured by a series circuit of several single p-n junctions. (c) Current voltage characteristics of Diode A for $T_L = 300\ \mathrm{K}$ (in equilibrium) and $80\ \mathrm{K}$ (under negative-illumination). The area of square $P_M$ corresponds to the maximum power generation under negative-illumination.
• Figure 3: Diode temperature dependence of photovoltage of a single p-n junction $-v_{OC} = -V_{OC}/N$ (a), zero-bias resistance of a single p-n junction for unit area $r_D S$ (b), inherent photocurrent density $I_{SC}/S$, and maximum power generation density $p_{M}/S$ (d). The cold bath temperature $T_L$ is kept in the range between $80$ and $85\ \mathrm{K}$.
• Figure 4: (a) External quantum efficiency $\eta_Q$ and energy conversion efficiency $\eta_E$ as a function of inverse diode temperature. (b) Theoretical prediction of $\eta_E$ as a function of $r_D S$.