In the pursuit of harnessing albedo energy, bifacial photovoltaic (PV) devices emerge as a beacon of innovation. Perovskite solar cells (PSCs) are particularly adept in low-light conditions, displaying superior open-circuit voltage and minimal voltage loss, thus effectively capitalizing on albedo energy.

For peak bifacial performance, electrodes must be optically transparent, chemically stable, and harmonious with adjacent layers. Traditional materials like indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) are hindered by their inherent brittleness, limiting their use in flexible applications. Additionally, the fabrication of transparent conducting oxides (TCOs) as back electrodes poses a significant challenge; the high-temperature deposition process risks compromising the delicate perovskite layers.

Addressing these limitations, our latest publication in Nature Communications introduces a feasible approach: employing single-walled carbon nanotubes (SWCNTs) as both front and back electrodes. This innovation not only promises enhanced transparency and conductivity but also ensures compatibility with the perovskite layer, heralding a new era for flexible, efficient bifacial PSCs.

Optical and electrical characterizations (Figure 1) underscore the exceptional attributes of SWCNT films, positioning them as prime candidates for transparent electrodes in bifacial PSCs. Their remarkable optical transmittance and conductivity, coupled with a high G to D band intensity ratio (IG/ID = 162), signal high crystallinity and minimal defects, enhancing charge transport efficiency. Ultraviolet photoelectron spectroscopy reveals the SWCNT films’ work function to be approximately is about -4.70 eV, on par with ITO, underscoring their potential as a superior alternative in terms of work function, sheet resistance, and optical transmittance.

We then prepared bifacial devices by using SWCNT as both front and back electrodes and measured the corresponding performances (Figure 2). The resultant PSCs have demonstrated enhanced power generation density (PGD) under different albedo conditions. By removing ITO and back metal electrodes, the stability of these carbon-based devices has improved greatly. These results underscore the potential of SWCNT electrodes to create efficient and stable bifacial PSCs, promising a significant step forward in solar technology.  

Power generation simulations (Figure 3) of bifacial PSCs for 2025 project a peak energy yield of 35 kWh in June, leveraging high sunlight exposure. Over a 26-year horizon, these PSCs are expected to deliver an annual output of 300 kWh. The integration of carbon materials in bifacial PSCs notably enhances energy generation, especially in urban landscapes rich in reflective glass surfaces, optimizing the harnessing of solar energy.