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Colourful solar panels could be on the way


Over the past decade, countless new buildings have had photovoltaic (PV) arrays integrated into their design in an effort to improve sustainability and lower environmental footprint. The decreasing cost of such arrays has seen PVs retrofitted onto many existing rooftops and facades. Economically, building-integrated solar power is big business. But aesthetically, it leaves a lot to be desired, with architects regularly describing conventional PV units as “pretty ugly”, or an eyesore. In a very real way, their appearance acts as barrier to their wider adoption in architecture. 

But group of Chinese researchers may have found a way to make PV systems more eye-catching. In a paper published in Nano Energy [DOI: 10.1016/j.nanoen.2021.105937] they report on a series of prototype cells that reflect light in colours that stretch across the entire visible spectrum. Their colourful cells are based on PEDOT:PSS/Si heterojunctions – films of conductive polymer coated onto polished silicon wafers. And unlike the multi-coloured p-n junction silicon solar cells that were first developed in 2004, these do not require complicated processing approaches or additional functional layers to achieve a variety of colour.

Instead, the colour of the final cell results from adjusting both the thickness of the PEDOT:PSS layer and its refractive index. The thickness acts as a sort of wavelength selector, enhancing a specific wavelength while suppressing others. As a result, a series of cells with a different polymer layer thicknesses would appear as different colours when illuminated by white light. Through modelling the interaction, the authors found tuning the thickness could “only realize a narrow color range, which is far away from the vivid visual sense.” To expand the range of available colours, and obtain the saturated, vivid colours they desired, they realised they’d need to adjust the optical properties of the polymer itself. For this, they chose to vary the porosity of the film, which they achieved through changing the doping material used in the poylmer’s preparation.

Triton X-100, a commonly-used lab surfactant, was the first to be tested. Increasing its concentration in the PEDOT:PSS film decreased the overall refractive index, which led to highly-saturated red and orange PV devices. However, this same addition made the device less efficient at turning light into electricity – the pink cell had an efficiency of 10.62 %. In contrast, films doped with molybdenum trioxide (MoO3) gradually shifted towards blue-purple part of the spectrum as the concentration (and refractive index) increased. Devices made with MoO3 had higher photoelectric conversion efficiencies, with the purple cell reaching a peak of 13.2 %. 

The authors say that “the method reported here can be readily scaled up using mature industrial tools such as inkjet printers,” and that it “offers a practical method to fabricate aesthetically appealing and yet efficient photovoltaic solar cells.”


This story was written for Materials Today:

Research paper: Lei-Ming Yu, Jia-Xiu Man, Tao Chen, Deying Luo, Juan Wang, Hannan Yang, Yong-Biao Zhao, Hai Wang, Yu Yang, Zheng-Hong Lu. “Colorful conducting polymers for vivid solar panels”, Nano Energy 85 (2021) 105937. DOI: 10.1016/j.nanoen.2021.105937