Abstract
The direct conversion of solar radiation into electricity is an abundant, clean and renewable approach for the production of energy. The organic/inorganic trihalide perovskites have shown an auspicious opportunity for the development of cost effective and efficient solar cells, owing to their unique optoelectronic characteristics. Although the developed perovskite solar cells exhibited efficiency reached to 20%, the hysteresis, device stability and toxicity of lead are serious problems hindering their commercialization. Here, we report about the partial replacement of lead ions by lanthanum ions in the crystal structure of the organic/inorganic trihalide perovskites. The photovoltaic performance of the FTO/b-TiO2/mp-TiO2/CH3NH3[LaxPb1-x]I-3/NiO/Au at various contents of La ions (0 <= x <= 0.07) was evaluated. Among all developed devices, the FTO/b-TiO2/mp-TiO2/CH3NH3[La0.07Pb0.93]I-3/NiO/Au device exhibited the highest short-circuit current density (J(sc) = 19.53 mA.cm(-2)) and largest open-circuit voltage (V-oc = 0.9 V). This device exhibited remarkable air stability with retaining 96% of the PCE, FE, V-oc and J(sc) along four months under ambient environmental conditions. This device showed a significant reduction of the I-V hysteresis compared to un-doped device. The reason for such improvement of the photocurrent, stability and reduction of hysteresis was argued to the strong chemical bonds formed between the La ions and the nitrogen and lead atoms as confirmed by the IR spectroscopy and the increase of perovskite grains as indicated from the XRD and SEM measurements.