Mahui

A near‐infrared non‐fullerene acceptor BTTIC is well compatible with different bandgap polymers, i.e., J71 (1.92 eV), PBDB‐T (1.80 eV), and PTB7‐Th (1.58 eV), which achieves power conversion efficiencies (PCEs) as high as 12.8%, 13.2%, and 10.4%, with fill factors all over 70%, suggesting BTTIC is a promising non‐fullerene acceptor for polymers selectivity.

Owing to their good polymer compatibility, fullerene derivatives, such as PC₆₁BM and PC₇₁BM, have been the dominant electron acceptors to pair with various polymer donors in polymer solar cells (PSCs). The recent surge of non‐fullerene materials leads to several high‐performance molecular acceptors. Despite their high performance in a given polymer/acceptor system, the generality of these acceptors, i.e., their compatibility with different donor polymers remains uncertain. Here, a high‐performance small molecule acceptor (SMA), BTTIC, is designed and synthesized to combine with three polymers with different bandgaps, namely J71 (1.92 eV), PBDB‐T (1.80 eV), and PTB7‐Th (1.58 eV). Complementary absorption, compatible energy levels, and particularly the favorable morphologies between BTTIC and the three polymers enable high power conversion efficiencies (PCEs), which are 12.8%, 13.2%, and 10.4% for J71:BTTIC‐, PBDB‐T:BTTIC‐, and PTB7‐Th:BTTIC‐based PSCs, respectively, significantly higher than the PCEs of the fullerene‐ or other non‐fullerene‐based counterparts. Moreover, another famous p‐type polymer donor PffBT4T‐2OD, which shows poor solubility in chloroform and has not yet been studied in non‐fullerene PSCs, is also investigated. Processing by dissolving PffBT4T‐2OD and BTTIC in boiling chloroform enables PffBT4T‐2OD:BTTIC‐based PSCs with a PCE of 10.18%, which is significantly higher than that of PSCs (4.78%) before using boiling chloroform processing. The good compatibility of BTTIC with polymers that have either large, moderate, or small bandgaps makes it a promising non‐fullerene acceptor for next‐generation non‐fullerene PSCs.

Molecular additive engineering using chlorine‐based compounds such as formamidinium chloride reduces the bulk and surface carrier recombination and improves the crystallinity of the perovskite film, resulting in solar cell devices with high efficiency exceeding 21% and great stability.

Abstract

The presence of surface and grain boundary defects in organic–inorganic halide perovskite films can be detrimental to both the performance and operational stability of perovskite solar cells (PSCs). Here, the effect of chloride additives is studied on the bulk and surface defects of the mixed cation and halide PSCs. It is found that using an antisolvent technique, the perovskite film is divided into two layers, i.e., a bottom layer with large grains and a thin capping layer with small grains. The addition of formamidinium chloride (FACl) into the precursor solution removes the small‐grained perovskite capping layer and suppresses the formation of bulk and surface defects, providing a perovskite film with enhanced crystallinity and large grain size of over 1 µm. Time‐resolved photoluminescence measurements show longer lifetimes for perovskite films modified by FACl and subsequently passivated by 1‐adamantylamine hydrochloride as compared to the reference sample. Impedance spectroscopy measurements show that these treatments reduce the recombination in the PSCs, leading to a champion device with power conversion efficiency (PCE) of 21.2%, an open circuit voltage of 1152 mV and negligible hysteresis. The Cl treated PSC also shows improved operational stability with only 12% PCE loss after 700 h under continuous illumination.

The elemental sulfur (S₈) added to the perovskite precursor solution ((FAPbI₃)_0.95(MAPbBr₃)_0.05 in dimethylformamide/dimethyl sulfoxide) not only increases the stability of the solution owing to amine–sulfur coordination but also significantly improves the thermalstability and photostability due to the increase in chemical stability of the perovskite material itself without compromising the power conversion efficiency of the resulting perovskite solar cells.

Abstract

Efficient perovskite solar cells (PSCs) are mainly fabricated by a solution coating processes. However, the efficiency of such devices varies significantly with the aging time of the precursor solution used to fabricate them, which includes a mixture of perovskite components, especially methylammonium (MA), and formamidinium (FA) cations. Herein, how the inorganic–organic hybrid perovskite precursor solution of (FAPbI₃)_0.95(MAPbBr₃)_0.05 degrades over time and how such degradation can be effectively inhibited is reported on, and the associated mechanism of degradation is discussed. Such degradation of the precursor solution is closely related to the loss of MA cations dissolved in the FA solution through the deprotonation of MA to volatile methylamine (CH₃NH₂). Addition of elemental sulfur (S₈) drastically stabilizes the precursor solution owing to amine–sulfur coordination, without compromising the power conversion efficiency (PCE) of the derived PSCs. Furthermore, sulfur introduced to stabilize the precursor solution results in improved PSC stability.

Prospects for low-toxicity lead-free perovskite solar cells

Prospects for low-toxicity lead-free perovskite solar cells, Published online: 27 February 2019; doi:10.1038/s41467-019-08918-3

Continuous wave amplified spontaneous emission in phase-stable lead halide perovskites

Continuous wave amplified spontaneous emission in phase-stable lead halide perovskites, Published online: 28 February 2019; doi:10.1038/s41467-019-08929-0

Unveiling the operation mechanism of layered perovskite solar cells

Unveiling the operation mechanism of layered perovskite solar cells, Published online: 01 March 2019; doi:10.1038/s41467-019-08958-9

Bi‐doped MAPbI₃ perovskite can simultaneously improve the Seebeck coefficient and electrical conductivity. It not only promotes the charge transport through carrier channels near grain boundaries, but can also passivate the defects, increasing the stability of MASnI₃.

Abstract

In this article, the thermoelectric properties of a Bi‐doped CH₃NH₃PbI₃ (MAPbI₃) perovskite thin film are studied. Bi‐doped MAPbI₃ thin film samples are fabricated, and it is found that Bi doping could greatly enhance the stability and thermoelectric properties of MAPbI₃. The Bi dopant located at the grain boundaries to modify the carrier channel near grain boundaries, which is observed via scanning electron microscopy and atomic force microscopy, efficiently reduces ion migration and facilitates charge transport. In addition, the Bi dopant can also passivate the defects in bulk MAPbI₃, increasing the polarization effect of MAPbI₃ which is demonstrated by the capacitance‐frequency measurement, thus greatly enhancing the mobility of Bi‐doped MAPbI₃. In addition, Bi‐doped MAPbI₃ leads to grain size reduction; the small size effect not only effectively hinders the MAPbI₃'s crystal phase transition from the tetragonal phase to the cubic phase, but it could also make the structure of MAPbI₃ more stable. Especially, the Seebeck voltage variation of Bi‐doped perovskite was less than that of the undoped one, meaning Bi doping would lead to a much more stable state in MAPbI₃ thin films. The results show that Bi‐doped MAPbI₃ is a promising approach to develop high stable thermoelectric and photovoltaic properties in organic–inorganic hybrid perovskite materials.