The lattice defects in the bulk and on the surface of the halide perovskite layer serve as trap sites and recombination centers to annihilate photogenerated carriers, determining the performance and stability of perovskite optoelectronic devices. Herein, the previously reported surface defects passivation engineering is extended to a full defects passivation strategy through stereoscopically introducing the cysteamine hydrochloride (CSA‐Cl) in the bulk and on the surface of perovskites. First‐principle density functional theory (DFT) calculations are employed to theoretically verify the multiple defects passivation effect of the CAS‐Cl on the perovskite. The perovskite layer with full defects passivation exhibits superior carrier dynamics as revealed by femtosecond transient absorption due to the reduced defect density determined by a highly sensitive photothermal deflection spectroscopy technique. Consequently, a high efficiency approaching 21% is achieved for the inverted planar perovskite solar cells (PVSCs). More importantly, the CAS‐Cl passivated PVSCs exhibit operation in air, which will be beneficial for the in situ device test for understanding the photophysics involved. This work provides a promising strategy to reduce the defects in both the perovskite bulk and surface for superior optoelectronic properties, facilitating the development of highly efficient and stable PVSCs and other optoelectronic devices.

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Directional solution coating by the Chinese brush provides a facile approach to fabricate highly oriented polymer thin films by finely controlling the wetting and dewetting processes under directional stress. The biggest advantage of the Chinese brush over the normal western brush is the freshly emergent hairs used, whose unique tapered structure renders a dynamic balance of the liquid within the brush by multiple forces when interacting with the liquid. Consequently, the liquid is steadily held within the brush without any unexpected leakage, making the liquid transfer proceed in a well-controllable manner. It is demonstrated that the Chinese brush coating enables the crystallization of the polymer and the self-assembly of conjugated backbones to proceed in a quasi-steady state via a certain direction, which is attributed to the controllable receding of the three-phase contact line during the dewetting process by the multiple parallel freshly emergent hairs. The as-prepared polymer thin films exhibit over six times higher charge-carrier mobility compared to the spin-coated films, which therefore provides a general approach for high-performance organic thin-film transistors.

Passivation of organometal halide perovskites with polar molecules has been recently demonstrated to improve the photovoltaic device efficiency and stability. However, the mechanism is still elusive. Here, it is found that both polymers with large and small dipole moment of 3.7 D and 0.6 D have negligible defect passivation effect on the MAPbI 3 perovskite films as evidenced by photo thermal deflection spectroscopy. The photovoltaic devices with and without the polymer additives also have comparable power conversion efficiencies around 19%. However, devices with the additives have noticeable improvement in stability under continuous light irradiation. It is found that although the initial mobile ion concentrations are comparable in both devices with and without the additives, the additives can strongly suppress the ion migration during the device operation. This contributes to the significantly enhanced electrical-field stress tolerance of the perovskite solar cells (PVSCs). The PVSCs with polymer additives can operate up to −2 V reverse voltage bias which is much larger than the breakdown voltage of −0.5 V that has been commonly observed. This study provides insight into the role of additives in perovskites and the corresponding device degradation mechanism.

Tandem solar cells (SCs) based on perovskite and silicon represent an exciting possibility for a breakthrough in photovoltaics, enhancing SC power conversion efficiency (PCE) beyond the single-junction limit while keeping the production cost low. A critical aspect to push the tandem PCE close to its theoretical limit is the development of high-performing semitransparent perovskite top cells, which also allow suitable near-infrared transmission. Here, we have developed highly efficient semitransparent perovskite SCs (PSCs) based on both mesoporous and planar architectures, employing Cs0.05(MA0.17FA0.83)0.95Pb­(I0.83Br0.17)3 and FA0.87Cs0.13PbI2Br perovskites with band gaps of 1.58 and 1.72 eV, respectively, which achieved PCEs well above 17 and 14% by detailed control of the deposition methods, thickness, and optical transparency of the interlayers and the semitransparent electrode. By combining our champion 1.58 eV PSCs (PCE of 17.7%) with an industrial-relevant low-cost n-type Si SCs, a four-terminal (4T) tandem efficiency of 25.5% has been achieved. Moreover, for the first time, 4T tandem SCs’ performances have been measured in the low light intensity regime, achieving a PCE of 26.6%, corresponding to revealing a relative improvement above 9% compared to the standard 1 sun illumination condition. These results are very promising for their implementation under field-operating conditions.