Evidence for surface defect passivation as the origin of the remarkable photostability of unencapsulated perovskite solar cells employing aminovaleric acid as a processing additive

Abstract

AVA can passivate surface defect sites, resulting in enhanced resistivity to oxygen/light induced degradation.

Investigating the Superoxide Formation and Stability in Mesoporous Carbon Perovskite Solar Cells with an Aminovaleric Acid Additive

“…Whether the absorptance is corrected by shifting it so that the absorptance at 850 nm is zero, or not, does not significantly affect the corrected superoxide yield (Figures S15–S19, Supporting Information). The corrected superoxide yield I ( t )/ I ( t = 0) at 660 nm shows that glass/AVA‐MAPI generates more superoxide than glass/MAPI on the timescale studied ( Figure ), consistent with the recent work of Lin et al24 Although AVA‐MAPI has been reported to have a lower defect concentration than MAPI,24 the smaller size of the crystals of AVA‐MAPI lead to an increase surface/volume ratio which may increase the overall defect concentration of AVA‐MAPI compared to MAPI, and thus may explain the higher superoxide yield measured. The variations of the probe fluorescence without a sample present were recorded twice as a baseline for our experiments.…”

“…If the perovskite is deposited on a moderate bandgap semiconductor (e.g., titanium oxide, TiO 2 ), electrons can be extracted at a faster rate than the rate of the reaction with oxygen reducing the quantity of superoxide formed, thus inhibiting this degradation pathway. Superoxide formation is only the first step of oxygen‐mediated degradation of perovskite and although a material can generate more superoxide than another, it may be more sensitive to superoxide as reported previously 24…”

“…A year later, Mei et al mixed MAPI with 5‐aminovaleric acid [5‐AVA, NH 2 (CH 2 ) 4 CO 2 H] to improve the penetration and distribution of the perovskite within the stack which resulted in a (5‐AVA) x (MA) 1− x PbI 3 based device with an improved PCE of 12.8% 31. It was also suggested that this improved penetration and surface contact resulted in lower defect concentration 24,31. 5‐AVA affects the crystal structure of the MAPI by forming hydrogen bonds between its carboxyl (COOH) and ammonia (NH 3 + ) groups and the iodide ions of MAPI 31.…”

Origin of Open‐Circuit Voltage Enhancements in Planar Perovskite Solar Cells Induced by Addition of Bulky Organic Cations

“…This class of perovskite films were termed quasi 3D perovskites by Hu et al, with there being little evidence of 2D structure formation . Studies of such perovskite devices, where a low concentration of bulky organic spacer cation is incorporated into the 3D structure, have reported both high performance and enhanced stability . The enhanced performance of these devices has primarily been due to improved V oc , whereas a reduced current density ( J sc ) has also been observed in several studies .…”

Passivating Detrimental DX Centers in CH3NH3PbI3 for Reducing Nonradiative Recombination and Elongating Carrier Lifetime

“…[4,12,[14][15][16][17][18][19] In the conventional picture of semiconductor defects, V I is a shallow donor and usually positively charged. [4,12,[14][15][16][17][18][19] In the conventional picture of semiconductor defects, V I is a shallow donor and usually positively charged.…”