Detao Liu

Interface engineering of high efficiency perovskite solar cells based on ZnO nanorods using atomic layer deposition

Despite the considerably improved efficiency of inorganic–organic metal hybrid perovskite solar cells (PSCs), electron transport is still a challenging issue. In this paper, we report the use of ZnO nanorods prepared by hydrothermal self-assembly as the electron transport layer in perovskite solar cells. The efficiency of the perovskite solar cells is significantly enhanced by passivating the interfacial defects via atomic layer deposition of Al2O3 monolayers on the ZnO nanorods. By employing the Al2O3 monolayers, the average power conversion efficiency of methylammonium lead iodide PSCs was increased from 10.33% to 15.06%, and the highest efficiency obtained was 16.08%. We suggest that the passivation of defects using the atomic layer deposition of monolayers might provide a new pathway for the improvement of all types of PSCs..

Solvent annealing of PbI2 for the high-quality crystallization of perovskite films for solar cells with efficiencies exceeding 18%

While most work carried out to date has focused on the solvent annealing of perovskite, in the present work, we focused on the solvent annealing of lead iodide. Based on the two-step spin-coating method, we designed a screening method to search for an effective solvent annealing process for PbI2. PbI2 films were annealed in diverse solvent atmospheres, including DMF, DMSO, acetone, and isopropanol (IPA). We found that the solvent annealing of PbI2 in the DMF, acetone, and IPA atmospheres resulted in dense PbI2 films, which impeded the complete conversion of PbI2 to CH3NH3PbI3. Surprisingly, employing the DMSO solvent annealing process for PbI2 led to porous PbI2, which facilitated the complete conversion of PbI2 to perovskite with larger grain sizes. Solar cells fabricated using the DMSO solvent annealing process exhibited the best efficiency of 18.5%, with a fill factor of 76.5%. This unique solvent annealing method presents a new way of controlling the perovskite film quality for highly efficient solar cells.

Perovskite Solar Cells with ZnO Electron‐Transporting Materials

Perovskite solar cells (PSCs) have developed rapidly over the past few years, and the power conversion efficiency of PSCs has exceeded 20%. Such high performance can be attributed to the unique properties of perovskite materials, such as high absorption over the visible range and long diffusion length. Due to the different diffusion lengths of holes and electrons, electron transporting materials (ETMs) used in PSCs play a critical role in PSCs performance. As an alternative to TiO2 ETM, ZnO materials have similar physical properties to TiO2 but with much higher electron mobility. In addition, there are many simple and facile methods to fabricate ZnO nanomaterials with low cost and energy consumption. This review focuses on recent developments in the use of ZnO ETM for PSCs. The fabrication methods of ZnO materials are briefly introduced. The influence of different ZnO ETMs on performance of PSCs is then reviewed. The limitations of ZnO ETM-based PSCs and some solutions to these challenges are also discussed. The review provides a systematic and comprehensive understanding of the influence of different ZnO ETMs on PSCs performance and potentially motivates further development of PSCs by extending the knowledge of ZnO-based PSCs to TiO2 -based PSCs.

Enhanced efficiency and environmental stability of planar perovskite solar cells by suppressing photocatalytic decomposition

The environmental instability of perovskite solar cells caused by the ultraviolet photocatalytic effect of metal oxide layers is a critical issue that must be solved. In this paper, we report improved environmental stability of ZnO film-based planar heterojunction perovskite solar cells, by suppressing photocatalytic activities induced by the ZnO electron transfer layer. The photovoltaic performance and stability in an ambient environment under continuous illumination are effectively improved by applying an aluminum oxide interlayer on the ZnO film to suppress the photocatalytic degradation of perovskites. The highest efficiency of solar cells has increased from 14.62% to 17.17%, and after 250 h of continuous exposure under full spectrum simulated sunlight in air, the efficiency remains as high as 15.03%. The results suggest that effective suppression of photocatalytic degradation of perovskites with a modified electron transfer layer is a new solution to improve the long-term environmental stability of perovskite solar cells.

Enhanced electronic transport in Fe3+-doped TiO2 for high efficiency perovskite solar cells

Oxygen vacancies in non-stoichiometric TiO2 electron transport layers can capture injected electrons and act as recombination centers. In this study, the compact TiO2 electron transport layers of perovskite solar cells (PSCs) are doped with different molar ratios of Fe3+ in order to passivate such defects and improve their electron transport properties. The electrical conductivity, absorption, crystal structure, and the performance of the PSCs are systematically studied. It shows that Fe3+-doping improves the conductivity of TiO2 compact layers compared with the pristine TiO2, boosting the photovoltaic performance of PSCs. The reduced trap-filled limit voltage (VTFL) of the Fe3+-doped TiO2 compact layers suggests that trap density in the Fe3+-TiO2 films is much lower than that of a pristine TiO2 film. With the optimized doping concentration (1 mol%) of Fe3+, the best power conversion efficiency of PSCs is improved from 16.02% to 18.60%.

Enhanced Performance of Planar Perovskite Solar Cells Using Low-Temperature Solution-Processed Al-Doped SnO2 as Electron Transport Layers

Lead halide perovskite solar cells (PSCs) appear to be the ideal future candidate for photovoltaic applications owing to the rapid development in recent years. The electron transport layers (ETLs) prepared by low-temperature process are essential for widespread implementation and large-scale commercialization of PSCs. Here, we report an effective approach for producing planar PSCs with Al3+ doped SnO2 ETLs prepared by using a low-temperature solution-processed method. The Al dopant in SnO2 enhanced the charge transport behavior of planar PSCs and increased the current density of the devices, compared with the undoped SnO2 ETLs. Moreover, the enhanced electrical property also improved the fill factors (FF) and power conversion efficiency (PCE) of the solar cells. This study has indicated that the low-temperature solution-processed Al-SnO2 is a promising ETL for commercialization of planar PSCs.

Realizing Full Coverage of Stable Perovskite Film by Modified Anti-Solvent Process

Lead-free solution-processed solid-state photovoltaic devices based on formamidinium tin triiodide (FASnI3) and cesium tin triiodide (CsSnI3) perovskite semiconductor as the light harvester are reported. In this letter, we used solvent engineering and anti-solvent dripping method to fabricate perovskite films. SnCl2 was used as an inhibitor of Sn4+ in FASnI3 precursor solution. We obtained the best films under the function of toluene or chlorobenzene in anti-solvent dripping method and monitored the oxidation of FASnI3 films in air. We chose SnF2 as an additive of CsSnI3 precursor solution to prevent the oxidation of the Sn2+, improving the stability of CsSnI3. The experimental results we obtained can pave the way for lead-free tin-based perovskite solar cells (PSCs).

Reveal the growth mechanism in perovskite films via weakly coordinating solvent annealing

In this study, we investigated the nucleation mechanism of perovskite films by employing isopropanol (IPA), a weakly coordinating solvent, to anneal both PbI2 and CH3NH3PbI3 in the sequential deposition and CsPbI3 in the one-step deposition. IPA solvent annealing (IPA SA) of PbI2 films was carried out at different temperatures. The grain size, compactness, roughness and morphology of PbI2 and CH3NH3PbI3 films were seriously affected by annealing methods. Similarly, weakly coordinating solvent annealing process was also employed to anneal all inorganic CsPbI3 perovskite in a one-step method. A continuous and dense CsPbI3 film with uniform grain size was obtained. We recognized that weakly coordinating solvent annealing for perovskite could regulate the dissolution-recrystallization process via controlling the volume of residual solvent in perovskite intermediate films. The power conversion efficiency (PCE) of conventional CH3NH3PbI3 perovskite solar cells (PSCs) reached 17.4% and that of CsPbI3 PSCs reached 2.5% based on this sequential IPA SA process.摘要本研究在两步法沉积CH3NH3PbI3和一步法沉积CsPbI3薄膜过程中使用弱配位溶剂异丙醇(IPA)对钙钛矿及钙钛矿前驱体进行溶剂退火处理, 从而揭示了钙钛矿薄膜的成核机理. 同时研究了退火温度对两步法中PbI2前驱体进行溶剂退火处理时的作用. 发现IPA溶剂退 火工艺严重影响了PbI2和CH3NH3PbI3薄膜的晶粒尺寸、 致密度、 粗糙度和薄膜形貌. 相同的弱配位溶剂退火工艺也被应用于制备全无机CsPbI3钙钛矿. 通过溶剂退火可以得到具有均匀晶粒尺寸、 连续致密的全无机CsPbI3薄膜. 我们认为弱配位溶剂退火工艺可以通过有效地调控钙钛矿中间相中的残留溶剂量来影响钙钛矿成膜中的再结晶过程. 通过IPA溶剂退火工艺, CH3NH3PbI3钙钛矿太阳能电池光电转换效率达到17.4%, 而CsPbI3的光电转换效率达到了2.5%.