Doping effects in SnO2 transport material for high performance planar perovskite solar cells

Planar heterojunction perovskite solar cells have emerged as competitive photovoltaic technology, where charge transport materials play a crucial role. Here, we successfully demonstrate a systematic approach to investigate the doping effect on SnO2 electron transport material, based on the introduction of metal chloride with different valance states. A thorough characterization by x-ray diffraction, x-ray photoelectron spectroscopy, space charge limited current, transmittance, time-resolved photoluminescence and electrochemical impedance spectroscopy measurements was performed to gain an understanding of the SnO2-based materials and devices. It was revealed that proper doping in the electron transport layer can benefit VOC and/or JSC in the devices, due to improved crystallinity, conductivity and transmittance, along with faster interface transfer. Further analysis indicates that certain doping elements are increasingly beneficial to cell performance, which follows the sequence of Li, Mg and Sb. We present here the overall performance improvement from the original efficiency of 15.48% to an elevated one as 17.07% with our Sb-doped SnO2 cell. The enhancement in conductivity also confirms that p-type doping for SnO2 in this case can still be favorable. Furthermore, the entire device was fabricated via a solution process with the processing temperature below 200 °C, suggesting a promising way toward the further development of low-cost perovskite solar cells and commercial manufacturing.