CrystEngComm Blog

The race is on to develop the most efficient, low-cost solar cells to meet the green energy demand of the future. Unfortunately, high power conversion efficiencies often come at high economic cost and so there is still a lot of room for improvement for existing materials and technologies.

Scientists from Donghua University, China, have now touched upon another desirable feature of solar cell materials – environmentally friendly synthesis. Junqing Hu and his team have sought to develop solar cells based on Cu₂ZnSnS₄ (CZTS) nanocrystal films.

Previous reports using these nanocrystal inks or the selenised CZTSSe analogues have shown promise but their hydrophobic nature (due to the oleylamine capping agent) means they can only be dispersed in organic solvents. Other drawbacks to their synthesis include using cadmium in the buffer layer (environmental implications); glass substrates (inflexibility); and hydrazine as a precursor to the inks (toxic and difficult to handle).

In their recent CrystEngComm Communication, Hu and colleagues describe the solvothermal synthesis of hydrophilic CZTS nanocrystal inks. By developing a film-printing technique they were able to fabricate a flexible and environmentally-friendly solar cell. Although the conversion efficiency is somewhat low (1.94 %) compared to other reported values for CZTSSe materials, the authors expect that it can be improved by optimising the film-printing technique, film thickness and annealing process, and selenising the film.

This HOT article is free to access until 19^th March so download it now…

Hydrophilic Cu₂ZnSnS₄ nanocrystals for printing flexible, low-cost and environmentally friendly solar cells
Qiwei Tian,  Xiaofeng Xu,  Linbo Han,  Minghua Tang,  Rujia Zou,  Zhigang Chen,  Muhuo Yu,  Jianmao Yang and Junqing Hu

Perovskite materials are pretty tricky to synthesise – particularly those with A_xA_1–x‘BO₃ structure. Conventional solid state approaches suffer from contamination with unreacted materials and even sol-gel processes can result in materials with structural defects and impurities.

Chi-Young Lee and co-workers from National Tsing Hua University in Taiwan have set out to find a simpler route to synthesise these troublesome materials, developing a chemical method that requires the lowest temperature reported to date for perovskite synthesis.

Their method involves mixing TiO₂ with the desired Group 2 hydroxide in sodium hydroxide solution and refluxing at 140 °C. By varying the reaction time, they were able to control the morphology as they demonstrated for SrTiO₃, attributing the different forms to the relative stabilities of the crystal planes. What’s more, they could tune the composition of Ba_xSr_1–xTiO₃ through stoichiometric adjustment of the starting materials.

To find out more on Lee and his team’s perovskite synthesis, download the CrystEngComm article today…
Simple chemical preparation of perovskite-based materials using alkali treatment

Also of interest…

• Local structural distortion of BaZr_xTi_1–xO₃ nanocrystals synthesized at room temperature, F. A. Rabuffetti and R. L. Brutchey, Chem. Commun., 2012, 48, 1437.
• Low-temperature synthesis of solid-solution Ba_xSr_1–xTiO₃ nanocrystals, R. L. Brutchey et al., J. Mater. Chem., 2010, 20, 5074.