Improvement of green antisolvent-isopropanol and additive-thiourea on carbon based CsPbIBr2 perovskite solar cells

In recent years, all-inorganic perovskite cells (PSCs) have been widely studied by researchers because of their excellent thermal and optical stability. Among them, the CsPbIBr2 PSCs with carbon electrode have attracted extensive attention because of its excellent stability, low preparation difficulty, easy commercialization and low cost. However, the crystal quality of CsPbIBr2 film is poor. There are a large number of pinholes and surface defects (Pb2+ exposure), which will lead to internal short circuit and a large number of nonradiative recombination, thus affecting the photoelectric conversion efficiency (PCE). Although these problems can be improved by antisolvent engineering, the traditional antisolvent chlorobenzene (CB) and toluene (TL) are highly toxic and harmful to the environment. In this paper, isopropanol (IPA) is used as a green antisolvent to improve the quality of CsPbIBr2 films, and S2− with strong reducibility and passivation defects are successfully introduced into the CsPbIBr2 film surface by further adding thiourea as Lewis base to IPA (IPA-S). After the CsPbIBr2 films were treatment by IPA-S antisolvent, we successfully obtained high-quality CsPbIBr2 films with large grain size and no pinholes. Moreover, through XPS, PL, EIS and other tests, it is found that the S2− introduced by IPA-S can combine with the exposed Pb2+ on the CsPbIBr2 surface to passivate the defects, it is beneficial to reduce the non-radiative recombination and improve the transport capacity of carriers. Finally, the results of this paper prove that that the champion PCE of carbon based CsPbIBr2 PSCs treated with IPA-S antisolvent was 6.79%, which was nearly 30% higher than the original carbon based CsPbIBr2 PSCs. In addition, due to the strong reducibility of S2−, the carbon based CsPbIBr2 PSCs treated with isopropanol antisolvent added with thiourea can continue to work in air with 40% relative humidity, and the efficiency can remain 85% within 10 days. In order to improve the performance and stability of the all-inorganic PSCs, this paper provides a non-toxic, environmentally friendly and effective scheme.