Seamless Interfacial Formation by Solution-Processed Amorphous Hydroxide Semiconductor for Highly Efficient Electron Transport

Reducing the energy barriers for charge carrier injection, extraction, or transport within both electron- and hole-transporting interfaces is crucial for minimizing charge carrier transport losses in perovskite solar cells (PSCs). In this Article, an ultrafast, solution-processed hydroxide semiconductor material, called Nb(OH)5, which has a similar energy band and transparency to its crystallization, Nb2O5, is first used as an electron transport layer (ESL) for PSCs. The conductivity of the Nb(OH)5 is lower than that of Nb2O5; however, a power conversion efficiency (PCE) of approximately 13.62% is obtained by fully fabricating devices at room temperature with a MAPbI3 light absorption layer, which is almost the same as that of PSCs based on Nb2O5. The performance of the fabricated device shows that the Nb(OH)5 film has seamless contact with the fluorine-doped tin oxide (FTO) substrate. The conductivity of the Nb2O5 film is 4 orders larger than that of Nb(OH)5; however, a low interfacial barrier results in interfacial resistance between the Nb(OH)5 and FTO substrate that is 3–4 orders lower than that of Nb2O5 due to universal quasi-ohmic contacts. By comparing with properties of PSCs with different ESLs (Nb(OH)5 and Nb2O5), a further efficient electron extract principle from the perovskite layer to FTO substrate is promoted. The PCE of PSCs still needs to be improved further; however, this solution-processed hydroxide semiconductor material, Nb(OH)5, has shown numerous benefits to PSCs with ultrafast process, low cost, and large-area fabrication.