RESUMEN
The reverse bias stability is a key concern for the commercialization and reliability of halide perovskite photovoltaics. Here, the robustness of perovskite-silicon tandem solar cells to reverse bias electrical degradation down to -40 V is investigated. The two-terminal tandem configuration, with the perovskite coupled to silicon, can improve the solar cell resistance to severe negative voltages when the tandem device is properly designed. While perovskite cells typically exhibit early reverse bias breakdown voltages, the serial connection with silicon cells with large shunt resistances and high voltage breakdown limits their negative polarization and prevent the passage of large current densities when reverse biased. The importance of careful optical design is illustrated, with bottom-limited conditions required to prevent the perovskite top cell from exploring its own breakdown. This aspect is of great importance in the case of partial shading events when the solar spectrum is richer in the IR components than the standard AM1.5G. Notably, 100% of efficiency retained after polarization at -40 V in different stressing conditions is observed. The results presented suggest that standard industrial bypass diode schemes may be compatible with silicon/perovskite tandem photovoltaics and provide new guidelines for the standardization of the stressing protocols.
RESUMEN
To improve the performance of solar photovoltaic devices one should mitigate three types of losses: optical, electrical and thermal. However, further reducing the optical and electrical losses in modern photovoltaic devices is becoming increasingly costly. Therefore, there is a rising interest in minimizing the thermal losses. These correspond to the reduction in electrical power output resultant of working at temperatures above 25 °C and the associated accelerated aging. Here, we quantify the impact of all possible strategies to mitigate thermal losses in the case of the mainstream crystalline silicon technology. Results indicate that ensuring a minimum level of conductive/convective cooling capabilities is essential. We show that sub-bandgap reflection and radiative cooling are strategies worth pursuing and recommend further field testing in real-time operating conditions. The general method we propose is suitable for every photovoltaic technology to guide the research focused on reducing thermal losses.
RESUMEN
Multijunction cells may offer a cost-effective route to boost the efficiency of industrial photovoltaics. For any technology to be deployed in the field, its performance under actual operating conditions is extremely important. In this perspective, we evaluate the impact of spectrum, light intensity, and module temperature variations on the efficiency of tandem devices with crystalline silicon bottom cells with a particular focus on perovskite top cells. We consider devices with different efficiencies and calculate their energy yields using field data from Denver. We find that annual losses due to differences between operating conditions and standard test conditions are similar for single-junction and four-terminal tandem devices. The additional loss for the two-terminal tandem configuration caused by current mismatch reduces its performance ratio by only 1.7% when an optimal top cell bandgap is used. Additionally, the unusual bandgap temperature dependence of perovskites is shown to have a positive, compensating effect on current mismatch.
RESUMEN
The impacts of radiative, electrical and thermal losses on the performances of nanoscale-gap thermophotovoltaic (nano-TPV) power generators consisting of a gallium antimonide cell paired with a broadband tungsten and a radiatively-optimized Drude radiator are analyzed. Results reveal that surface mode mediated nano-TPV power generation with the Drude radiator outperforms the tungsten radiator, dominated by frustrated modes, only for a vacuum gap thickness of 10 nm and if both electrical and thermal losses are neglected. The key limiting factors for the Drude- and tungsten-based devices are respectively the recombination of electron-hole pairs at the cell surface and thermalization of radiation with energy larger than the cell absorption bandgap. A design guideline is also proposed where a high energy cutoff above which radiation has a net negative effect on nano-TPV power output due to thermal losses is determined. It is shown that the power output of a tungsten-based device increases by 6.5% while the cell temperature decreases by 30 K when applying a high energy cutoff at 1.45 eV. This work demonstrates that design and optimization of nano-TPV devices must account for radiative, electrical and thermal losses.