Abstract
Perovskite solar cells have exhibited astonishing photoelectric conversion efficiency and have shown a promising future owing to the tunable content and outstanding optoelectrical property of hybrid perovskite. However, the devices with planar architecture still suffer from huge Voc loss and severe hysteresis effect. In this research, Guanidine hydrobromide (GABr) post-treatment is carried out to enhance the performance of MAPbI3 n-i-p planar perovskite solar cells. The detailed characterization of perovskite suggests that GABr post-treatment results in a smoother absorber layer, an obvious reduction of trap states and optimized energy level alignment. By utilizing GABr post-treatment, the Voc loss is reduced, and the hysteresis effect is alleviated effectively in MAPbI3 solar cells. As a result, solar cells based on glass substrate with efficiency exceeding 20%, Voc of 1.13 V and significantly mitigated hysteresis are fabricated successfully. Significantly, we also demonstrate the effectiveness of GABr post-treatment in flexible device, whose efficiency is enhanced from 15.77% to 17.57% mainly due to the elimination of Voc loss.
Highlights
Organic–inorganic hybrid perovskites have received great attention due to their superior properties of high light absorption coefficient [1], low exciton binding energy [2], and long diffusion length [3], which are suitable for application in photovoltaic devices.Lead-based organic perovskite (APbX3, A = CH3 NH3 +, CH(NH2 )2 +, alkali metal ion or mixed cations; X = I, Cl, Br or mixed anions) is easy to fabricate and the power conversion efficiency (PCE) for the state-of-the-art device has achieved 25.5% [4]
12.78◦ is assigned to PbI2, which disappears after Guanidine hydrobromide (GABr) treatment [37,38]
GA+ might locate at the grain boundary or the surface of the perovskite layer, rather than entering the lattice of MAPbI3 because there is no obvious shift observed in MAPbI3 peaks
Summary
MAPbI3 is the commonly used material in perovskite solar cell (PSCs) with lower Urbach. The development of MAPbI3 -based PSCs is rapid, but the device performance still suffers from nonnegligible nonradiative recombination [8,9]. MAPbI3 is compatible with various fabrication techniques, and among which the solution process is commonly taken in experiments due to the advantage of low temperature and easy operation. The film deposited through solution method is usually polycrystalline with high density of defects situated at the grain boundary or the film surface, which act as nonradiative recombination centers and result in serious efficiency loss [10,11,12,13,14]. The existence of defects will induce ion migration in perovskite layer and cause serious hysteresis in solar cells which brings difficulty in determining the accurate efficiency of PSCs [15,16]
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