We build a double quantum-dot system with Coulomb coupling and aim at studying connections among the entropy production, free energy, and information flow. By utilizing concepts in stochastic thermodynamics and graph theory analysis, Clausius and nonequilibrium free energy inequalities are built to interpret local second law of thermodynamics for subsystems. A fundamental set of cycle fluxes and affinities is identified to decompose two inequalities by using Schnakenberg’s network theory. Results show that the thermodynamic irreversibility has energy-related and information-related contributions. A global cycle associated with the feedback-induced information flow would pump electrons against the bias voltage, which implements a Maxwell demon.

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A new scheme of near-field thermophotovoltaic devices is proposed by introducing the intermediate-band absorber. The two-step excitation via the intermediate band provides a large photogenerated current density and maintains a high voltage output for the thermal-electric conversion. Energy dissipation processes in devices are analyzed by using the detailed balance model. Results show that the powers and efficiencies of thermophotovoltaic devices with intermediate bands in appropriate positions are clearly larger than those of the conventional counterparts. Based on the optical properties observed in experiments, three types of absorber materials are compared, which indicates that InAs with low energy bandgap is more suitable as a high-temperature material for photon absorptions than GaSb and Si. Comparing the performance of our model with experiments, we show that the InAs based thermophotovoltaic device allows the enhancement of efficiency over a range of gap sizes. The proposed model may open a new field in the application of thermophotovoltaic devices.

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A solar-driven charging device composed of a photovoltaic module and a supercapacitor is proposed. Based on the equivalent circuit model of the device, the current–voltage relationship of the hybrid system is established. The energy conversion and storage efficiency and the energy stored in the supercapacitor as functions of the charging time have been derived. The advantage of the theoretical model is that the effects of the series resistance, parallel resistance, solar irradiance, and operating temperature on the charging performance of the supercapacitor can be evaluated. The optimal relationships between the capacitance of the supercapacitor and the charging time at different external conditions, i.e., the optimally matching conditions of the supercapacitor, have been provided. Results show that the proposed theoretical analysis method is capable of efficiently evaluating the performance of photo-supercapacitors under given parameters of practical photovoltaic systems. The proposed model may pave the foundation for the future development of supercapacitors driven by commercial PV modules.