Yaohua Mai

Controllable Grain Morphology of Perovskite Absorber Film by Molecular Self-Assembly toward Efficient Solar Cell Exceeding 17%

The highly developed crystallization process with respect to perovskite thin films is favorable for efficient solar cells. Here, an innovative intermolecular self-assembly approach was employed to retard the crystallization of PbI2 in dimethylformamide (DMF) by additional solvent of dimethyl sulfoxide (DMSO), which was proved to be capable of coordinating with PbI2 by coordinate covalent bond. The obtained PbI2(DMSO)x (0 ≤ x ≤ 1.86) complexes tend to be closely packed by means of intermolecular self-assembly. Afterward, an intramolecular exchange of DMSO with CH3NH3I (MAI) enabled the complexes to deform their shape and finally to reorganize to be an ultraflat and dense thin film of CH3NH3PbI3. The controllable grain morphology of perovskite thin film allows obtaining a power conversion efficiency (PCE) above 17% and a stabilized power output above 16% within 240 s by controlling DMSO species in the complex-precursor system (CPS). The present study gives a reproductive and facile strategy toward high quality of perovskite thin films and efficient solar cells.

Hysteretic Behavior upon Light Soaking in Perovskite Solar Cells Prepared via Modified Vapor-Assisted Solution Process.

Recently, the organic-inorganic hybrid perovskite solar cells exhibit rapidly rising efficiencies, while anomalous hysteresis in perovskite solar cells remains unsolvable. Herein, a high-quality perovskite thin film is prepared by a modified vapor-assisted solution process, which is a simple but well-controllable method proven to be capable of producing a thin film with full surface coverage and grain size up to micrometers. The as-fabricated perovskite solar cell has efficiency as high as 10.2%. The hysteresis effects of both planar and mesoscopic TiO2-based perovskite solar cells have been comprehensively studied upon illumination. The results demonstrate that mesoporous-based perovskite cells combined with remarkable grain size are subject to alleviating the hysteresis effects in comparison to the planar cells. Likewise, mesoscopic TiO2-based perovskite cells perform independently of illumination and bias conditions prior to the measurements, whereas the planar cells display a reversible behavior of illumination and applied bias-dependent I-V curves. The present study would refer strip road for the stability study of the perovskite solar cells.

Highly Efficient Perovskite Solar Cells with Substantial Reduction of Lead Content

Despite organometal halide perovskite solar cells have recently exhibited a significant leap in efficiency, the Sn-based perovskite solar cells still suffer from low efficiency. Here, a series homogeneous CH3NH3Pb(1−x)SnxI3 (0u2009≤u2009xu2009≤u20091) perovskite thin films with full coverage were obtained via solvent engineering. In particular, the intermediate complexes of PbI2/(SnI2)∙(DMSO)x were proved to retard the crystallization of CH3NH3SnI3, thus allowing the realization of high quality Sn-introduced perovskite thin films. The external quantum efficiency (EQE) of as-prepared solar cells were demonstrated to extend a broad absorption minimum over 50% in the wavelength range from 350 to 950 nm accompanied by a noteworthy absorption onset up to 1050u2009nm. The CH3NH3Pb0.75Sn0.25I3 perovskite solar cells with inverted structure were consequently realized with maximum power conversion efficiency (PCE) of 14.12%.

All-Inorganic CsPbI2Br Perovskite Solar Cells with High Efficiency Exceeding 13%

All-inorganic perovskite solar cells provide a promising solution to tackle the thermal instability problem of organic-inorganic perovskite solar cells (PSCs). Herein, we designed an all-inorganic perovskite solar cell with novel structure (FTO/NiO x/CsPbI2Br/ZnO@C60/Ag), in which ZnO@C60 bilayer was utilized as the electron-transporting layers that demonstrated high carrier extraction efficiency and low leakage loss. Consequently, the as-fabricated all-inorganic CsPbI2Br perovskite solar cell yielded a power conversion efficiency (PCE) as high as 13.3% with a Voc of 1.14 V, Jsc of 15.2 mA·cm-2, and FF of 0.77. The corresponding stabilized power output (SPO) of the device was demonstrated to be ∼12% and remarkably stable within 1000 s. Importantly, the obtained all-inorganic PSCs without encapsulation exhibited only 20% PCE loss with thermal treatment at 85 °C for 360 h, which largely outperformed the organic-species-containing PSCs. The present study demonstrates potential in overcoming the intractable issue concerning the thermal instability of perovskite solar cells.

Addictive-assisted construction of all-inorganic CsSnIBr2 mesoscopic perovskite solar cells with superior thermal stability up to 473 K

The poor stability of hybrid organic–inorganic perovskite is one of crucial problems limiting the practical application of the perovskite solar cells (PSCs). All-inorganic lead-free perovskite materials, with Cs replacing the organic cations and Sn replacing Pb, have shown great potential in achieving high thermal stability. However, tin-based perovskites have inevitably suffered from severe bulk recombination, attributed to Sn vacancies. In this work, we obtain CsSnIBr2 thin films with low Sn vacancy assisted by the addition of hypophosphorous acid (HPA). The HPA additive here as complexant is demonstrated to be capable of speeding up the nucleation process while inhibiting the formation of Sn4+ during the formation process of CsSnIBr2 thin films. With a mesoscopic architecture, the CsSnIBr2 PSCs exhibit efficiency-loss free in 77 days and remarkably stable power output within 9 hours at high temperatures up to 473 K.

Efficiency enhancement of Sb2Se3 thin-film solar cells by the co-evaporation of Se and Sb2Se3

In this work, we present an alternative route to supply excessive selenium (Se) for the deposition of Sb2Se3 thin films by the co-evaporation of Se and Sb2Se3. Scanning electron microscopy (SEM) images showed that additional Se modified the growth process and surface morphology of Sb2Se3 thin films. X-ray diffraction (XRD) patterns confirmed that this co-evaporation process enhanced the beneficiary preferred orientations, and capacitance–voltage (C–V) measurement showed that the carrier concentration of the Sb2Se3 absorber increased with the additional evaporation of Se. Accordingly, the efficiency of the devices employing co-evaporated Sb2Se3 absorber layers increased significantly from 2.1 to 3.47% with a open-circuit voltage (V OC) of 364 mV, a short-circuit current density (J SC) of 23.14 mA/cm2, and a fill factor (FF) of 41.26%.

Magnesium thin film as a doping-free back surface field layer for hybrid solar cells

In this work, a magnesium (Mg) thin film with a low work function is introduced to obtain a downward energy band at the rear surface of a hybrid solar cell to achieve the function of a back surface field (BSF) similar to the conventional n-n+ high-low junction, i.e., favouring the majority carrier transport and suppressing minority carrier recombination. The open circuit voltages (Voc) of the hybrid solar cells with the Mg BSF layer achieve a clear improvement over those containing only the conventional metal electrode (e.g., Ag), resulting in an increase in the power conversion efficiency (PCE) of the hybrid solar cells from 9.2% to 12.3%. The Suns-Voc measurement determined using a Sinton tool gives Voc as a function of light intensity and shows that Voc increases linearly with the light intensity for the solar cell with the Mg BSF but increases first and then stabilises for the cells without the Mg BSF. This result is attributed to a difference in back surface recombination, further confirming the effi...

Silicon surface passivation by polystyrenesulfonate thin films

The use of polystyrenesulfonate (PSS) thin films in a high-quality passivation scheme involving the suppression of minority carrier recombination at the silicon surface is presented. PSS has been used as a dispersant for aqueous poly-3,4-ethylenedioxythiophene. In this work, PSS is coated as a form of thin film on a Si surface. A millisecond level minority carrier lifetime on a high resistivity Si wafer is obtained. The film thickness, oxygen content, and relative humidity are found to be important factors affecting the passivation quality. While applied to low resistivity silicon wafers, which are widely used for photovoltaic cell fabrication, this scheme yields relatively shorter lifetime, for example, 2.40u2009ms on n-type and 2.05u2009ms on p-type wafers with a resistivity of 1–5 Ω·cm. However, these lifetimes are still high enough to obtain high implied open circuit voltages (Voc) of 708u2009mV and 697u2009mV for n-type and p-type wafers, respectively. The formation of oxides at the PSS/Si interface is suggested to ...

CdS/Sb2S3 heterojunction thin film solar cells with a thermally evaporated absorber

An antimony sulfide (Sb2S3) semiconductor is appealing as a promising light absorber due to its suitable bandgap (1.5–1.7 eV), ‘one dimensional’ crystal structure and non-toxic constituents. In this work, the orientation preferences of the Sb2S3 thin films grown on the CdS layer and bare glass substrates were compared by SEM and XRD measurements. The growth direction of (Sb4S6)n ribbons was found to be substrate-dependent, and the growth mechanism was discussed. Thin film solar cells in the configuration of glass/(SnO2:F) FTO/CdS/Sb2S3/Au were fabricated and the highest conversion efficiency reached 3.01%. The defects and recombination losses in the thin film solar cells were investigated by voltage-dependent quantum efficiency and time-resolved photoluminescence measurements. The CdS/Sb2S3 (n–p) heterojunction solar cells showed a little decrease by about 0.2% in conversion efficiency to 2.84% after three month storage in ambient air without encapsulation.

Solution-Processed One-Dimensional ZnO@CdS Heterojunction toward Efficient Cu2ZnSnS4 Solar Cell with Inverted Structure

Kesterite Cu2ZnSnS4 (CZTS) semiconductor has been demonstrated to be a promising alternative absorber in thin film solar cell in virtue of its earth-abundant, non-toxic element, suitable optical and electrical properties. Herein, a low-cost and non-toxic method that based on the thermal decomposition and reaction of metal-thiourea-oxygen sol-gel complexes to synthesize CZTS thin film was developed. The low-dimensional ZnO@CdS heterojunction nano-arrays coupling with the as-prepared CZTS thin film were employed to fabricate a novel solar cell with inverted structure. The vertically aligned nanowires (NWs) allow facilitating the charge carrier collection/separation/transfer with large interface areas. By optimizing the parameters including the annealing temperature of CZTS absorber, the thickness of CdS buffer layer and the morphology of ZnO NWs, an open-circuit voltage (VOC) as high as 589u2009mV was obtained by such solar cell with inverted structure. The all-solution-processed technic allows the realization of CZTS solar cell with extremely low cost.