Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP20)
Publication date: 14th October 2019
Perovskite solar cells (PVs) that consisting of APbX3 absorber layer (where A=Cs, FA, MA and B=I, Br) are very promising due to their high efficiency and low manufacturing cost. In particular, several reports have experimentally shown that the addition of KI into the precursor solution significantly improves the performance and suppress the hysteresis [1]. Although several mechanisms have already been suggested, our recent results on KI post-treatment of the upper surface of APbX3 absorber layer suggest a different mechanism leading to the passivation of I defects. Here, we shall present our results and discuss the possible mechanisms.
We fabricated and characterized Glass/FTO/ETL/APbX3/HTL/Au solar cells. ETL is compact/mesoporous TiO2 and HTL is spiro-OMeTAD (doped with TBP, Li-TFSI in AN). APbX3 was prepared using FAI, PbI2, MABr, PbBr2 dissolved in DMSO/DMF into which CsI dissolved in DMSO were added, as already reported. Furthermore, we performed the post-treatment of the upper surface of APbX3 absorber layer using KI dissolved in isopropanol (IPA). It is very important to stress that in contrast to the previous reports in which KI was added to the precursor solution [1] or substituted to CsI [2], here we performed the post-treatment of the upper surface of APbX3 absorber layer using KI/IPA. The IV curves of these PVs were recorded in forward and reverse direction (in the range -0.1~1.2 V, at various scan rate) under illumination (1sun, 100mW/cm2, A.M. 1.5, with 420nm UV cut filter, SAN-EI Electric XES-40S1 solar simulator).
We find that the KI/IPA post-treatment of APbX3 absorber layer show a significant improvement of Voc and PCE, as well as a complete suppression of hysteresis (at various scan speed), compare with untreated APbX3. In addition, time-resolved photoluminescence measurements show that the decay time constant increase upon KI/IPA treatment, which suggest a longer carrier lifetime and less recombination. Furthermore, X-ray didn’t reveal a sizable change of the diffraction pattern of the APbX3, which discard the insertion of K into APbX3 crystal structure. In addition, surface and cross-section SEM images didn’t reveal a sizable change of the microstructure of APbX3. Our results on KI/IPA post-treatment of the upper surface of APbX3 absorber layer suggest that the passivation of I defects at the surface and/or at the grain boundaries are the main reason. At this conference, we shall present our results and discuss the mechanisms in the light of the most recent results [1, 2, 3].
We acknowledge the grant from the New Energy and Industrial Technology Development Organization (NEDO, Japan).
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