Perovskite solar cells (PSCs) are one of the most promising lab-scale technologies to deliver inexpensive solar electricity. Low-temperature printable carbon counter electrode based planar-heterojunction PSCs are particularly suitable for future large-scale manufacturing, but suffer from an inferior efficiency. Here, we demonstrate a TiO2/SnO2 bilayer as the electron transport layer (ETL) for carbon counter electrode based planar-heterojunction PSCs together with micromolecule Cu-phthalocyanine (CuPc) as the hole transport layer (HTL), yielding a high power conversion efficiency of 15.39% and an excellent stability over 1200 h. The improved performances are attributed to a better energy level transition, a suppressed electron–hole recombination, and a wider depletion region of the TiO2/SnO2 bilayer. Our work represents a great advancement in the fabrication and popularization of carbon counter electrode based PSCs. More importantly, the whole devices are processed at a temperature below 200 °C, providing potential application of PSCs in monolithic tandem devices and paving the way for the development of carbon based flexible PSCs.
Combining two kinds of electron transport layer (ETL) which have complementary advantages into a bilayer structure to form a bilayer ETL is an effective way to transcend inherent limitations of single-layer ETL, which is very helpful in the development of perovskite solar cells (PSCs). In this work, a strategy is proposed to break constraints on the application of the staggered bilayer ETL in high-efficiency PSC, namely utilizing a built-in field to overcome the dilemma in E CBM making it possible to improve V OC and FF simultaneously by tuning the Fermi level of ETLs properly. According to the strategy, a bilayer ETL structure comprised of C-TiO 2 and SnO 2 layer and corresponding Li-doping process are developed, and the characterization results confirm the effectiveness of the strategy, making the potentials of the C-TiO 2 (Li)/SnO 2 bilayer ETL fully released for its application in high-efficiency PSCs: a V OC of 1.201 V for an ordinary triple-cation-perovskite-based PSC and a photoelectric conversion efficiency of 24.3% for a low-bandgap-perovskite-based PSC with high haze FTO superstrate are successfully achieved, indicating that the C-TiO 2 (Li)/SnO 2 bilayer ETL is a successful application paradigm of the proposed strategy and very promising in the application of high-efficiency PSCs.
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