A Biopolymer Heparin Sodium Interlayer Anchoring TiO₂ and MAPbI₃ Enhances Trap Passivation and Device Stability in Perovskite Solar Cells

Abstract

Traps in the photoactive layer or interface can critically influence photovoltaic device characteristics and stabilities. Here, traps passivation and retardation on device degradation for methylammonium lead trihalide (MAPbI ) perovskite solar cells enabled by a biopolymer heparin sodium (HS) interfacial layer is investigated. The incorporated HS boosts the power conversion efficiency from 17.2 to 20.1% with suppressed hysteresis and Shockley-Read-Hall recombination, which originates primarily from the passivation of traps near the interface between the perovskites and the TiO cathode. The incorporation of an HS interfacial layer also leads to a considerable retardation of device degradation, by which 85% of the initial performance is maintained after 70 d storage in ambient environment. Aided by density functional theory calculations, it is found that the passivation of MAPbI and TiO surfaces by HS occurs through the interactions of the functional groups (COO , SO , or Na ) in HS with undersaturated Pb and I ions in MAPbI and Ti in TiO . This work demonstrates a highly viable and facile interface strategy using biomaterials to afford high-performance and stable perovskite solar cells.

Efficient Bifacial Passivation with Crosslinked Thioctic Acid for High‐Performance Methylammonium Lead Iodide Perovskite Solar Cells

“…[18] Meanwhile, these trap states create conditions for the infiltration of moisture and oxygen into perovskite layer and subsequently seriously decrease the device stability. Additive engineering [26][27][28][29][30][31][32][33][34] and interface engineering [35][36][37][38][39][40][41] have been regarded as effective strategies to reduce the defect density in PSCs, such as incorporating Phenyl-C61-butyric acid methyl ester (PCBM) [29] into perovskite layer to effectively passivate the defects and minimize the photocurrent hysteresis, inserting self-assembled monolayer of organic molecules with functional groups [36,37] into perovskite/ETL interface to suppress defects Defects, inevitably produced within bulk and at perovskite-transport layer interfaces (PTLIs), are detrimental to power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). [23][24][25] Therefore, it is imperative to seek an effective way to reduce the defects, especially at the PTLIs, for achieving the high-performance PSCs.…”

“…For simplicity, there are two main binding groups of COOH and CS for the monomer TA in Poly(TA). In contrast, there are three kinds of adsorption configurations for TA molecule on MAPbI 3 surface, as shown in Figure 5b and Figure S13 As for the charge density differences of TA on the (110) oriented MAPbI 3 surface, [37,48] the COOH and CS groups are mainly responsible for the electron loss, while the peripheral lead atoms mainly capture electrons. [37] The adsorption energy is defined as E ads = E TiO2+TA -E TiO2 − E TA , where E TiO2+TA is the total energy of the TA molecule adsorbed on (110) plane of TiO 2 .…”

Interfacial Sulfur Functionalization Anchoring SnO2 and CH3NH3PbI3 for Enhanced Stability and Trap Passivation in Perovskite Solar Cells

“…We further measured timeresolved PL to analyze the charget ransport kinetics as shown in Figure 5b.T he decay curveso fp erovskite on SnO 2 or SnO 2 / Ss ubstrates are fitted with bi-exponential components,w here the fast (t 1 )d ecay is mainly correlated to interfacial charge transfer,a nd the slow (t 2 )d ecay was causedb yr adiative emissions of the bulk perovskite film involving trap-assisted recombination. [15] The decay fitting parameters are given in Ta ble S2. The fast decay (t 1 )o ft he perovskite decreased from 15.5 ns to 10.3 ns upon sulfur functionalization, indicating am ore rapid interfacial electron transfer from perovskite to ETL.…”

“…[8] So far,t here has been av ariety of organic interfacial modulationt echniques to mitigate the influence of defects on the charge transfer kinetics and energetically favorable rapid nucleation, such as use of amino acids and self-assembled monolayers (SAMs). [15,16] Electronic coupling betweent he SnO 2 ETL andp erovskite allows for efficient electron extraction and this reduces chargea ccumulation near the interface, [11,17] which results in strongh ysteresis behavior.T o Trap states at the interface or in bulk perovskite materials critically influence perovskite solar cells performance and longterm stability.H ere, as trategy for efficiently passivatingc harge traps and mitigating interfacial recombination by SnO 2 surface sulfur functionalization is reported, which utilizes xanthate decomposition on the SnO 2 surface at low temperature. [12,13] However,t hese approaches involved multiple and complex fabrication processes or using complicated organic molecules, which is not favorable in terms of fabrication cost.…”

“…Although complicated organic molecules [10,15] were employed to realize rapid charget ransfer at the interface and suppress hysteresis, potentiald efects in the interconnections among organicm olecules limit the effectiveness of the interfacial trap passivation, [14] which is unfavorable for photovoltaic device performance or stabilityi na mbient environment. Inorganic sulfur functionalization on the SnO 2 ETL was introduced through xanthate decomposition at low temperature to modify the SnO 2 /perovskite interface to anchor Pb 2 + in perovskite and SnO 2 simultaneously, leading to improved charge transport as ar esult of chemical interactions at the SnO 2 /perovskite junction.…”