Perceiving the temperature coefficients of carbon-based perovskite solar cells

Perovskite solar cells (PSCs) have emerged in a “catfish effect” of other established photovoltaic technologies with the rapid development of high-power conversion efficiency (PCE) and low-cost fabrication. Among various kinds of PSCs, organic hole transport layer (HTL)-free carbon-based PSCs (c-PSCs) have been considered as the most promising devices due to their excellent stability. However, temperature becomes one of the crucial factors in determining the pace of PSC commercialization. Temperature stress at the interface between the perovskite film and the charge transport layer is an essential factor in determining the performance of c-PSCs. This work assesses the correlation between the temperature coefficient (TC) and different photovoltaic parameters for HTL-free c-PSCs. To evaluate different photovoltaic parameters of the c-PSC as a function of temperature, two different testing approaches namely under steady temperature (ST) and transient temperature (TT) conditions have been considered across a wide temperature window (5–75 °C) under 1 Sun 1.5 AM. Here TT testing involves subjecting a single c-PSC to a continuous temperature treatment, whereas ST testing consists of specific temperature treatment of an individual c-PSC. The maximum efficiency achieved at 25 °C for TT testing devices is ∼14.5%, which is ∼11% higher than that of ST testing devices (PCE ∼ 13%). Moreover, the efficiency temperature coefficient (ETC) for ST testing was found to be 3.5 × 10−2 (5 °C ≤ T ≤ 25 °C) and −2.1 × 10−2 (25 °C ≤ T ≤ 75 °C), whereas the ETC values of TT testing devices were +2.5 × 10−2 (5 °C ≤ T ≤ 25 °C) and −1.8 × 10−2 (25 °C ≤ T ≤ 75 °C), respectively. The outcome of temperature stress transmitting through different interfacial layers was further investigated by thermal imaging of TT devices. On the other hand, X-ray diffraction and scanning electron microscopy structural analyses were performed to understand the effect of thermal stress on the overall performance of ST devices. It has been observed that TC values obtained under TT testing conditions are reversible, whereas in the case of ST testing the TC values are irreversible which shows degradation of the device.