Abstract
To obtain high performance CH3NH3PbI3 perovskite solar cells, it is highly important to realise a high open-circuit voltage. Calculation results based on a modified diode model have indicated that a low bare ratio ϕ of the perovskite film is the most important factor determining the open-circuit voltage, where ϕ is defined as the ratio of the projection of the uncovered area of the perovskite film to the apparent area of the total substrate surface. To realise a low ϕ, we investigate the nucleation behaviour of crystals on rough substrates. The analysis results predict that, when CH3NH3PbI3 is deposited on conventional transparent conductive oxide substrates such as fluorine-doped tin oxide, preferential heterogeneous nucleation will occur on the concave regions of the substrate; then, depending on the subsequent growth step, full coverage of the perovskite film at both the macroscopic and microscopic scales is realised. As a result, an ultra-high open-circuit voltage, i.e., 1.20 V, can be achieved in devices using the full coverage CH3NH3PbI3 film. The thermodynamics theory of precipitation nucleation should shed light on solution engineering of thin films.
Highlights
To obtain high performance CH3NH3PbI3 perovskite solar cells, it is highly important to realise a high open-circuit voltage
We further developed the thermodynamics theory of nucleation of perovskite on a rough substrate surface
We determine the correlation between the area of non-full coverage and the Voc value of planar Perovskite solar cells (PSCs) using the diode model
Summary
To obtain high performance CH3NH3PbI3 perovskite solar cells, it is highly important to realise a high open-circuit voltage. Calculation results based on a modified diode model have indicated that a low bare ratio φ of the perovskite film is the most important factor determining the open-circuit voltage, where φ is defined as the ratio of the projection of the uncovered area of the perovskite film to the apparent area of the total substrate surface. A high open-circuit voltage (Voc) is known to be important for obtaining high conversion efficiency. The ideal Voc is higher than the normally reported value of ~1.0 V9–12; it is vital to identify the factors determining Voc to realise a high Voc. The I−V properties of heterojunction solar cells can be analysed using the diode model[13,14]. In PSCs with planar configuration, which are more suitable for industrial roll-to-roll processes[19,20,21], the perovskite film is sandwiched between the electron transport layer and hole transport layer[22,23,24]
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