We demonstrated compact SnO2thin films prepared by sinter-less spin-coating processes as an electron selective contact for CH3NH3PbI3-based planar-heterojunction perovskite solar cells (PSCs).

Electron collection layer (ECL) is one of the most important fundamentals to determine the power conversion efficiency (PCE) in organometal halide-based perovskite solar cells (PSCs). Herein, we prepared ZnO-SnO 2 nanocomposites with different Zn/Sn ratios at low temperature as ECLs for CH 3 NH 3 PbI 3-based planar-structured PSCs. ZnO-SnO 2 nanocomposite with the optimal ~89 mol% of the ZnO content gives higher PCE than the ZnO for the best fabricated PSC. The photoluminescence spectroscopies measured in both steady and transient states and the electrochemical impedance spectroscopy were carried out to characterize the interface of CH 3 NH 3 PbI 3 and different ECLs, namely ZnO, ZnO-SnO 2 composite, and SnO 2. The high PCE of PSCs based on the ZnO-SnO 2 nanocomposite ECL was thus attributed to joint contributions of the high charge extraction efficiency and large charge recombination resistance both on the CH 3 NH 3 PbI 3 /ECL interface. The thermal stability of CH 3 NH 3 PbI 3 absorber and the device stability of the corresponding PSC are both dependent on the ECLs in the order: SnO 2 > ZnO-SnO 2 >ZnO, suggesting that the hydroxyl-induced degradation of CH 3 NH 3 PbI 3 may be predominant in the ambient air environment in the initial ~700 hours. The PCE of the optimized device was further improved to 15.2% by introducing the low-temperature processable Al 2 O 3 as a capping layer to the ZnO-SnO 2 composite.

The electron-selective contact layer (ESL) in organometal halide-based perovskite solar cells (PSCs) determines not only the power conversion efficiency (PCE) but also the thermostability of PSCs. To improve the thermostability of ZnO-based PSCs, we developed Mg-doped ZnO [Zn Mg O (ZMO)] as a high optical transmittance ESL for the methylammonium lead trihalide perovskite absorber [CH NH PbI ]. We further investigated the optical and electrical properties of the ESL films with Mg contents of 0-30 mol % and the corresponding devices. We achieved a maximum PCE of 16.5 % with improved thermal stability of CH NH PbI on ESL with the optimal ZMO (0.4 m) containing 10 mol % Mg. Moreover, this optimized ZMO PSC exhibited significantly improved durability and photostability owing to the improved chemical/photochemical stability of the wider optical bandgap ZMO.

ZnO thin films prepared by spin-coating of nanoparticles at low temperature were utilized as the electron collection layer in CH 3 NH 3 PbI 3 -based perovskite solar cells having a planar heterojunction structure. The thickness of ZnO layer as a key parameter to determine the photovoltaic performance was optimized. The highest power conversion efficiency of up to 13.9% with small hysteretic behavior of currentvoltage curves was achieved under AM 1.5 illumination (100 mW cm ¹2). The ZnO-based devices exhibited significantly improved durability as compared to the control device with exposure to the ambient air environment.Since the initial report in 2009, 1 organo-lead-halide-based perovskite solar cells (PSCs) have been attracting attention, and there has been great progress in this field.2 Intensive developments have elevated the power conversion efficiency (PCE) of PSCs to 19.6% within half a decade.3c Although a majority of PSCs are based on mesoporous TiO 2 requiring sintering at 500°C, parallel studies into low-temperature-processed PSCs for realizing a wearable/stretchable energy supplier are also in focus.3 In particular, ZnO-based PSCs are attractive owing to the following characteristics of ZnO materials: (1) ZnO is a wideband semiconductor having the band gaps and band energies similar to those of TiO 2 . (2) ZnO has higher electron mobility than TiO 2 .4 (3) Importantly, high crystallinity of ZnO could be attained without sintering processes. 5a Although some efficient PSCs based on ZnO have been reported so far, 5 their doubtable performance as indicated by the large hysteresis 5b from the photovoltaic behaviors and poor stability against ambient air suggest that further investigations are necessary. 6 In this study, we fabricated PSCs with ZnO electron collection layers that were processed at temperature of as low as 150°C. The effect of ZnO layer thickness on the device performance was investigated. Our results indicated that the ZnO-based PSCs can show high PCE with weak hysteretic behavior and excellent stability against ambient air without encapsulation.The ZnO nanoparticles used in this investigation were prepared according to procedures in the literature. 5a The ZnO nanoparticles were dispersed in butanol with a concentration of 6 mg mL ¹1 . The solution was spin-coated on ITO substrates to form a relatively compact ZnO layer and then heated at 150°for 5 min. This procedure could be repeated several times to obtain a certain thickness according to experimental requirements. A 460 mg mL ¹1 solution of PbI 2 in DMF was then spin-coated on top of the ZnO layer at 4000 rpm. After a short baking process at 70°C for 30 min, the substrate was dipped into a CH 3 NH 3 I solution (10 mg mL ¹1 in 2-propanol) for 50 s followed by heating at 70°C for 20 min to realize the desired crystallite formation. The details of fabrication and characterization of PSCs are described in the Supporting Information. Figure 1a schematically shows the device configuration of the PSCs studied in this investigation, and Fig...