In this paper, we aim to provide a power trade system that will promote a sustainable electrical energy transaction ecosystem between prosumers and consumers of smart homes. We suggest a blockchain-based peer-to-peer (P2P) energy transaction platform be implemented to enable efficient electrical energy transaction between prosumers. We suggest the platform be built on the blockchain, as this technology allows a decentralized and distributed trading system, and allows a more transparent, trustworthy and secure P2P trading environment. We believe that such characteristics of the blockchain are necessary in electrical energy transactions within the smart home environment because the smart home aims to enhance user comfort and security, along with energy conservation and cost-savings. First, we classify the two different types of P2P trade to identify which will best benefit from the use of the suggested blockchain-based P2P energy-transaction platform. Within the two types of P2P trade, that we classify (pure P2P trade and hybrid P2P trade), the hybrid P2P trade will benefit more from a blockchain-based P2P energy-transaction platform. In the blockchain-based P2P energy-transaction platform, a smart contract is embedded in the blockchain and called an energy tag. The energy tag will set conditions for making every future energy transaction more cost-efficient while maintaining the most ideal and high-quality energy selection. With the blockchain-based energy tag in the energy-transaction process, multiple energy resources and home appliances will be democratically connected in order to provide users with high-quality, low-cost energy at all times and locations. In this paper, we provide simulation results that compare the unit price of electrical energy on the suggested platform to the unit price of electrical energy set by currently existing conventional power-generation companies. Additionally, we present simulation results that calculate how long initial investments to create a smart home environment that enables P2P energy transactions will take to be paid back. Based on simulation results, we believe that, in the long run, the suggested blockchain-based P2P energy-transaction platform will create a sustainable energy-transaction environment between consumers and prosumers, and the expanding ecosystem will enable the development of a trusted, sustainable, secure and energy-efficient energy transaction environment.