Transparent integrated pyroelectric-photovoltaic structure for photo-thermo hybrid power generation

Abstract

Thermal losses in photoelectric devices limit their energy conversion efficiency, and cyclic input of energy coupled with pyroelectricity can overcome this limit. Here, incorporating a pyroelectric absorber into a photovoltaic heterostructure device enables efficient electricity generation by leveraging spontaneous polarization based on pulsed light-induced thermal changes. The proposed pyroelectric-photovoltaic device outperforms traditional photovoltaic devices by 2.5 times due to the long-range electric field that occurs under pulse illumination. Optimization of parameters such as pulse frequency, scan speed, and illumination wavelength enhances power harvesting, as demonstrated by a power conversion efficiency of 11.9% and an incident-photon-to-current conversion efficiency of 200% under optimized conditions. This breakthrough enables reconfigurable electrostatic devices and presents an opportunity to accelerate technology that surpasses conventional limits in energy generation.

Fig. 1. Transparent pyroelectric heterojunction device (TPHD).

a Carnot engine diagram, where Q_H (amount of heat) flows from a T_H (higher temperature) of the working substance and the Q_C (remaining heat) flows into the cold sink (T_C) to do work (W). b Steady (case I) and pulsed (case II) input energy for energy conversion. c Polarization versus electric field for transient signals illustrating the Brayton pyroelectric cycle. d Schematic depiction of TPHD, the built-in electric field at the ZnO/NiO heterojunction (photovoltaic-PV operation under steady illumination), and the long-range electric field function of dT/dt (pyroelectric-photovoltaic PE-PV operation under pulsed illumination). e Transmittance profile of the device and the photopic response. f Cross-section of the device, and g elemental line profile for Ag, Ni, Zn, Sn, F, and O.

Fig. 2. Polarization axis and photonic defects.

a Crystal structure of hexagonal ZnO, its lattice parameters (a–c), and polarization along the c-axis, in which pink and blue spheres represent Zn and O atoms, respectively, and orange sticks represent covalent bonds. High-resolution image of the device showing the b FTO/ZnO, c ZnO film, and d ZnO/NiO interfaces. e High-angle annular dark-field scanning transmission electron microscope image of the ZnO, middle of the device, overlain with the ZnO crystal cells, showing atomic defects of vacancies/points, interstitials, stained bonds, and voids. f The energy band of ZnO depicts optical excitation, defect modulation, carrier generation, and recombination. The Kroger Vink notation is used for interstitial (i), zinc (Zn), oxygen (O), and vacancy (V) states.

Fig. 3. Characteristic performance distribution under the illumination pulse.

a Schematic depiction of a TPHD unit cell and its array with a total of sixteen devices (4 × 4). b Original prototype TPHD array; the right panel shows the unit cell device and its electrical connection under pulsed light illumination. c Current-voltage characteristics and d power-voltage characteristics of the device under pulsed light illumination. Performance distribution of a total of sixteen devices showing the e short-circuit current density (J_SC) in μA cm⁻², f open-circuit voltage (V_OC) in V, g maximum power density (P_max) in μW cm⁻², h fill factor (FF) in %, i power conversion efficiency (PCE) in %, and j incident-photon-to-current conversion efficiency (IPCE) in %. PV and PE-PV represent photovoltaic and pyroelectric-photovoltaic operations, respectively.

Fig. 4. Influential parameters required to increase the pyroelectric-photovoltaic power.

a Energy band diagram of the device depicting the energy states of Zn and O vacancies ($V_{Zn}^{\prime }$/$V_{Zn}^X$, $V_{Zn}^{’’}$/$V_{Zn}^{\prime }$, $V_O^{\prime }$/$V_O^X$, $V_O^{’’}$/$V_O^{\prime }$), drift-diffusion segments of the heterojunction, built-in electric field (Ψ_bi) and long-range pyroelectric field (E_pyro) under pulsed illumination. E_C, E_V, and E_F represent the conduction band, valence band and Fermi energy levels, respectively. b Equivalent electrical circuits depicting transparent pyroelectric heterojunction device operation under steady darkness, upon illumination, under steady-light illumination, and in the dark state manifest photovoltaic and pyro-photovoltaic power reaping, where J, J_D, J_SC, J_PL, J_PD, R_S, and R_SH are the total current, diode current, short-circuit current, pyroelectric current upon light illumination, pyroelectric current in the dark, series resistance, and shunt resistance of the device, respectively. c Influential parameters of pulsed frequency (f) of light illumination, duty cycle (D), voltage scan speed (V s⁻¹), sample interval (μV), light wavelength (λ), device temperature (T), and pyro-coefficient (P_i). d P_max and PCE versus pulsed illumination frequency, f in Hz when the scan speed is 2 V s⁻¹ and the sample interval is 100 µV (error bar is 2.5%). e P_max and PCE versus scan speed in V s⁻¹ when the pulsed illumination rate ‘f’ is 60 Hz and the sample interval is 3 μV (error bar is 5%). f P_max and PCE versus sample interval at μV for a pulsed illumination rate of 60 Hz and a scan speed of 2 V s⁻¹ (error bar is 5%). g P_max and PCE versus duty cycle in % when the pulsed illumination f is 50 Hz, the scan speed is 0.5 V s⁻¹, and the sample interval is 10 ^μV (error bar is 2.5%). The illumination intensity was 2 mW cm⁻² during the frequency, scan speed, and sample interval studies.

Fig. 5. Photovoltaic spectral characteristics and pyroelectric coefficient.

Spectral characteristic performance, a power conversion efficiency (PCE) and b incident-photon-to-current conversion efficiency (IPCE) versus illumination wavelength (error bar is 5%). The device performance as a function of temperature, c PCE, and d IPCE versus temperature T at °C for an illumination wavelength of 365 nm and an intensity of 100 μW cm⁻² (error bar is 5%). During the spectral and thermal tests, the illumination f, scan speed, and sample interval were 60 Hz, 0.5 V s⁻¹, and 3μV, respectively. e Pyro-photoresponse of the device at 25, 50, and 65 °C for an illumination wavelength of 365 nm, intensity of 1.5 mW cm⁻², and pulse frequency of 1000 Hz. f Polarization current for the peak − peak, photo, and pyro intervals. g Pyroelectric coefficient, P_i distribution of ZnO and ZnO/NiO. h Comparison of the pyroelectric coefficients and figures of merit of the devices with those of conventional and emerging pyroelectric materials. (The pyroelectric coefficient and FOM data for conventional, bulk, and emerging materials are taken from ref. ^,).